Support of non-HEVC base layer in HEVC multi-layer extensions

ABSTRACT

An apparatus configured to decode video information includes a memory and a processor in communication with the memory. The memory is configured to a memory configured to store video information associated with bitstream. The apparatus further includes a processor in communication with the memory, the processor configured to determine that a reference layer is not included in the bitstream and to receive, from an external source, a decoded base layer picture. The processor is further configured to receive, from the external source, a first indication that the picture is an intra random access point (IRAP) picture. The processor is also configured to receive a second indication whether the picture is one of an instantaneous decoder refresh (IDR) picture, a clean random access (CRA) picture, or a broken link access (BLA) picture; and to decode the video information based at least in part on the first and second indications.

INCORPORATION BY REFERENCE TO PRIORITY APPLICATION(S)

This application claims priority to U.S. Provisional No. 61/925,149,filed Jan. 8, 2014.

TECHNICAL FIELD

This disclosure relates to the field of video coding and compression,particularly to scalable video coding (SVC), multiview video coding(MVC), or three-dimensional (3D) video coding.

BACKGROUND

Digital video capabilities can be incorporated into a wide range ofdevices, including digital televisions, digital direct broadcastsystems, wireless broadcast systems, personal digital assistants (PDAs),laptop or desktop computers, digital cameras, digital recording devices,digital media players, video gaming devices, video game consoles,cellular or satellite radio telephones, video teleconferencing devices,and the like. Digital video devices implement video compressiontechniques, such as those described in the standards defined by MPEG-2,MPEG-4, ITU-T H.263, ITU-T H.264/MPEG-4, Part 10, Advanced Video Coding(AVC), the High Efficiency Video Coding (HEVC) standard presently underdevelopment, and extensions of such standards. The video devices maytransmit, receive, encode, decode, and/or store digital videoinformation more efficiently by implementing such video codingtechniques.

Video compression techniques perform spatial (intra-picture) predictionand/or temporal (inter-picture) prediction to reduce or removeredundancy inherent in video sequences. For block-based video coding, avideo slice (e.g., a video frame, a portion of a video frame, etc.) maybe partitioned into video blocks, which may also be referred to astreeblocks, coding units (CUs) and/or coding nodes. Video blocks in anintra-coded (I) slice of a picture are encoded using spatial predictionwith respect to reference samples in neighboring blocks in the samepicture. Video blocks in an inter-coded (P or B) slice of a picture mayuse spatial prediction with respect to reference samples in neighboringblocks in the same picture or temporal prediction with respect toreference samples in other reference pictures. Pictures may be referredto as frames, and reference pictures may be referred to as referenceframes.

Spatial or temporal prediction results in a predictive block for a blockto be coded. Residual data represents pixel differences between theoriginal block to be coded and the predictive block. An inter-codedblock is encoded according to a motion vector that points to a block ofreference samples forming the predictive block, and the residual dataindicating the difference between the coded block and the predictiveblock. An intra-coded block is encoded according to an intra-coding modeand the residual data. For further compression, the residual data may betransformed from the pixel domain to a transform domain, resulting inresidual transform coefficients, which then may be quantized. Thequantized transform coefficients, initially arranged in atwo-dimensional array, may be scanned in order to produce aone-dimensional vector of transform coefficients, and entropy encodingmay be applied to achieve even more compression.

SUMMARY

Scalable video coding (SVC) refers to video coding in which a base layer(BL), sometimes referred to as a reference layer (RL), and one or morescalable enhancement layers (ELs) are used. In SVC, the BL can carryvideo data with a base level of quality. The one or more ELs can carryadditional video data to support, for example, higher spatial, temporal,and/or signal-to-noise (SNR) levels. ELs may be defined relative to apreviously encoded layer. For example, a bottom layer may serve as a BL,while a top layer may serve as an EL. Middle layers may serve as eitherELs or RLs, or both. For example, a layer in the middle may be an EL forthe layers below it, such as the BL or any intervening ELs, and at thesame time serve as a RL for one or more ELs above it. Similarly, in theMultiview or 3D extension of the HEVC standard, there may be multipleviews, and information of one view may be utilized to code (e.g., encodeor decode) the information of another view (e.g., motion estimation,motion vector prediction and/or other redundancies).

In SVC, a current block in the EL may be coded (e.g., encoded ordecoded) using the information derived from a RL. For example, a currentblock in the EL may be coded using the information (e.g., textureinformation or motion information) of a co-located block in the RL (theterm “co-located” as used in the present disclosure may refer to a blockin another layer that corresponds to the same image as the currentblock, e.g., the block that is currently being coded). In someimplementations, whether a particular RL is used to code an EL may besignaled as a flag or syntax element. If the flag or syntax elementindicates that the particular RL is used to code the EL, another flag orsyntax element may further be signaled to indicate what kind ofinformation in the particular reference picture is used to code the EL,such as, for example: texture (pixel) information, motion information,or both.

In certain cases, a portion of the information in the RL may not beavailable for use in coding the EL. For example, in someimplementations, if the RL is coded using a non-HEVC codec, the motioninformation of the RL may not be available to an HEVC codec to code theEL. In such a case, the EL may still be coded using the textureinformation of the RL, but the motion information of the RL cannot beused to code the EL.

By exploiting this dependence of the availability of certain types ofinformation in the RL on the type of codec used for coding the RL, someof the processing that is performed to determine what type ofinformation is derived from the RL may be omitted (e.g., if theinformation is unavailable, there is no need to check whether thatinformation is used for coding the EL), thus resulting in improvedcoding efficiency and/or reduced computational complexity.

The systems, methods and devices of this disclosure each have severalinnovative aspects, no single one of which is solely responsible for thedesirable attributes disclosed herein.

In one aspect, a method of decoding video information is provided. Themethod includes determining that a reference layer is not included in abitstream. The method further includes receiving, from an externalsource, a decoded base layer picture and receiving, from the externalsource, a first indication that the picture is an intra random accesspoint (IRAP) picture. The method further includes receiving a secondindication whether the picture is one of an instantaneous decoderrefresh (IDR) picture, a clean random access (CRA) picture, or a brokenlink access (BLA) picture and coding the video information based atleast in part on the first and second indications.

In some aspects, the reference layer may be decoded according to anon-HEVC (High Efficiency Video Coding) codec and/or an Advanced VideoCoding (AVC) codec. Determining whether the reference layer is includedin the bitstream may include determining whether the RL codec associatedwith the reference layer is the particular type of codec based upon avalue included in a one of a video parameter set, a sequence parameterset, a picture parameter set, or an adaptation parameter set. Theexternal source may be a second decoder, which may be configured todecode an AVC base layer. The indication may include a flag which may beset to either 1 or 0 to indicate that the picture is the IRAP picture.The second indication may include a variable with three or more possiblevalues.

One aspect of the present disclosure provides an apparatus configured todecode video information. The apparatus includes a memory configured tostore video information associated with a bitstream. The apparatusfurther includes a processor in communication with the memory. Theprocessor is configured to determine that a reference layer is notincluded in the bitstream. The processor is further configured toreceive, from an external source, a decoded base layer picture and toreceive, from the external source, a first indication that the pictureis an intra random access point (IRAP) picture. The processor is furtherconfigured to receive a second indication whether the picture is one ofan instantaneous decoder refresh (IDR) picture, a clean random access(CRA) picture, or a broken link access (BLA) picture and to decode thevideo information based at least in part on the first and secondindications.

In one aspect, a non-transitory computer readable medium is disclosed.The medium includes code that, when executed, causes an apparatus toperform a process. The process includes determining that a referencelayer is not included in a bitstream. The process further includesreceiving, from an external source, a decoded base layer picture andreceiving, from the external source, a first indication that the pictureis an intra random access point (IRAP) picture. The process furtherincludes receiving a second indication whether the picture is one of aninstantaneous decoder refresh (IDR) picture, a clean random access (CRA)picture, or a broken link access (BLA) picture, and decoding the videoinformation based at least in part on the first and second indications.

One aspect of the present disclosure provides a video decoding deviceconfigured to decode video information. The video decoding deviceincludes means for determining that a reference layer is not included ina bitstream. The device further includes means for receiving, from anexternal source, a decoded base layer picture and means for receiving,from the external source, a first indication that the picture is anintra random access point (IRAP) picture. The device further includesmeans for receiving a second indication whether the picture is one of aninstantaneous decoder refresh (IDR) picture, a clean random access (CRA)picture, or a broken link access (BLA) picture, and means for coding thevideo information based at least in part on the first and secondindications.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a block diagram illustrating an example video encoding anddecoding system that may utilize techniques in accordance with aspectsdescribed in this disclosure.

FIG. 1B is a block diagram illustrating another example video encodingand decoding system that may perform techniques in accordance withaspects described in this disclosure.

FIG. 2A is a block diagram illustrating an example of a video encoderthat may implement techniques in accordance with aspects described inthis disclosure.

FIG. 2B is a block diagram illustrating an example of a video encoderthat may implement techniques in accordance with aspects described inthis disclosure.

FIG. 3A is a block diagram illustrating an example of a video decoderthat may implement techniques in accordance with aspects described inthis disclosure.

FIG. 3B is a block diagram illustrating an example of a video decoderthat may implement techniques in accordance with aspects described inthis disclosure.

FIG. 4 illustrates a flow chart illustrating a method of coding videoinformation, according to one embodiment of the present disclosure.

FIG. 5 illustrates a flow chart illustrating a method of coding videoinformation, according to one embodiment of the present disclosure.

FIG. 6 illustrates a flow chart illustrating a method of coding videoinformation, according to one embodiment of the present disclosure.

FIG. 7 illustrates a flow chart illustrating a method of coding videoinformation, according to another embodiment of the present disclosure.

DETAILED DESCRIPTION

Certain embodiments described herein relate to inter-layer predictionfor scalable video coding in the context of advanced video codecs, suchas HEVC (High Efficiency Video Coding). More specifically, the presentdisclosure relates to systems and methods for improved performance ofinter-layer prediction in multi-layer video coding.

In the description below, H.264/AVC techniques related to certainembodiments are described; the HEVC standard and related techniques arealso discussed. While certain embodiments are described herein in thecontext of the HEVC and/or H.264 standards, one having ordinary skill inthe art may appreciate that systems and methods disclosed herein may beapplicable to any suitable video coding standard. For example,embodiments disclosed herein may be applicable to one or more of thefollowing standards: ITU-T H.261, ISO/IEC MPEG-1 Visual, ITU-T H.262 orISO/IEC MPEG-2 Visual, ITU-T H.263, ISO/IEC MPEG-4 Visual and ITU-TH.264 (also known as ISO/IEC MPEG-4 AVC), including its Scalable VideoCoding (SVC) and Multiview Video Coding (MVC) extensions.

HEVC generally follows the framework of previous video coding standardsin many respects. The unit of prediction in HEVC is different from thatin certain previous video coding standards (e.g., macroblock). In fact,the concept of macroblock does not exist in HEVC as understood incertain previous video coding standards. Macroblock is replaced by ahierarchical structure based on a quadtree scheme, which may providehigh flexibility, among other possible benefits. For example, within theHEVC scheme, three types of blocks, Coding Unit (CU), Prediction Unit(PU), and Transform Unit (TU), are defined. CU may refer to the basicunit of region splitting. CU may be considered analogous to the conceptof macroblock, but it does not restrict the maximum size and may allowrecursive splitting into four equal size CUs to improve the contentadaptivity. PU may be considered the basic unit of inter/intraprediction and it may contain multiple arbitrary shape partitions in asingle PU to effectively code irregular image patterns. TU may beconsidered the basic unit of transform. It can be defined independentlyfrom the PU; however, its size may be limited to the CU to which the TUbelongs. This separation of the block structure into three differentconcepts may allow each to be optimized according to its role, which mayresult in improved coding efficiency.

For purposes of illustration only, certain embodiments disclosed hereinare described with examples including only two layers (e.g., a lowerlayer such as the base layer, and a higher layer such as the enhancementlayer). It should be understood that such examples may be applicable toconfigurations including multiple base and/or enhancement layers. Inaddition, for ease of explanation, the following disclosure includes theterms “frames” or “blocks” with reference to certain embodiments.However, these terms are not meant to be limiting. For example, thetechniques described below can be used with any suitable video units,such as blocks (e.g., CU, PU, TU, macroblocks, etc.), slices, frames,etc.

Video Coding Standards

A digital image, such as a video image, a TV image, a still image or animage generated by a video recorder or a computer, may consist of pixelsor samples arranged in horizontal and vertical lines. The number ofpixels in a single image is typically in the tens of thousands. Eachpixel typically contains luminance and chrominance information. Withoutcompression, the quantity of information to be conveyed from an imageencoder to an image decoder is so enormous that it renders real-timeimage transmission impossible. To reduce the amount of information to betransmitted, a number of different compression methods, such as JPEG,MPEG and H.263 standards, have been developed.

Video coding standards include ITU-T H.261, ISO/IEC MPEG-1 Visual, ITU-TH.262 or ISO/IEC MPEG-2 Visual, ITU-T H.263, ISO/IEC MPEG-4 Visual andITU-T H.264, including its SVC and MVC extensions.

In addition, a new video coding standard, namely High Efficiency VideoCoding (HEVC), is being developed by the Joint Collaboration Team onVideo Coding (JCT-VC) of ITU-T Video Coding Experts Group (VCEG) andISO/IEC Motion Picture Experts Group (MPEG). The full citation for theHEVC Draft 10 is document JCTVC-L1003, Bross et al., “High EfficiencyVideo Coding (HEVC) Text Specification Draft 10,” Joint CollaborativeTeam on Video Coding (JCT-VC) of ITU-T SG16 WP3 and ISO/IECJTC1/SC29/WG11, 12th Meeting: Geneva, Switzerland, Jan. 14, 2013 to Jan.23, 2013. The multiview extension to HEVC, namely MV-HEVC, and thescalable extension to HEVC, named SHVC, are also being developed by theJCT-3V (ITU-T/ISO/IEC Joint Collaborative Team on 3D Video CodingExtension Development) and JCT-VC, respectively.

Various aspects of the novel systems, apparatuses, and methods aredescribed more fully hereinafter with reference to the accompanyingdrawings. This disclosure may, however, be embodied in many differentforms and should not be construed as limited to any specific structureor function presented throughout this disclosure. Rather, these aspectsare provided so that this disclosure will be thorough and complete, andwill fully convey the scope of the disclosure to those skilled in theart. Based on the teachings herein one skilled in the art shouldappreciate that the scope of the disclosure is intended to cover anyaspect of the novel systems, apparatuses, and methods disclosed herein,whether implemented independently of, or combined with, any other aspectof the present disclosure. For example, an apparatus may be implementedor a method may be practiced using any number of the aspects set forthherein. In addition, the scope of the present disclosure is intended tocover such an apparatus or method which is practiced using otherstructure, functionality, or structure and functionality in addition toor other than the various aspects of the present disclosure set forthherein. It should be understood that any aspect disclosed herein may beembodied by one or more elements of a claim.

Although particular aspects are described herein, many variations andpermutations of these aspects fall within the scope of the disclosure.Although some benefits and advantages of the preferred aspects arementioned, the scope of the disclosure is not intended to be limited toparticular benefits, uses, or objectives. Rather, aspects of thedisclosure are intended to be broadly applicable to different wirelesstechnologies, system configurations, networks, and transmissionprotocols, some of which are illustrated by way of example in thefigures and in the following description of the preferred aspects. Thedetailed description and drawings are merely illustrative of thedisclosure rather than limiting, the scope of the disclosure beingdefined by the appended claims and equivalents thereof.

The attached drawings illustrate examples. Elements indicated byreference numbers in the attached drawings correspond to elementsindicated by like reference numbers in the following description. Inthis disclosure, elements having names that start with ordinal words(e.g., “first,” “second,” “third,” and so on) do not necessarily implythat the elements have a particular order. Rather, such ordinal wordsare merely used to refer to different elements of a same or similartype.

Video Coding System

FIG. 1A is a block diagram that illustrates an example video codingsystem 10 that may utilize techniques in accordance with aspectsdescribed in this disclosure. As used described herein, the term “videocoder” refers generically to both video encoders and video decoders. Inthis disclosure, the terms “video coding” or “coding” may refergenerically to video encoding and video decoding. In addition to videoencoders and video decoders, the aspects described in the presentapplication may be extended to other related devices such as transcoders(e.g., devices that can decode a bitstream and re-encode anotherbitstream) and middleboxes (e.g., devices that can modify, transform,and/or otherwise manipulate a bitstream).

As shown in FIG. 1A, video coding system 10 includes a source module 12that generates encoded video data to be decoded at a later time by adestination module 14. In the example of FIG. 1A, the source module 12and destination module 14 are on separate devices—specifically, thesource module 12 is part of a source device, and the destination module14 is part of a destination device. It is noted, however, that thesource and destination modules 12, 14 may be on or part of the samedevice, as shown in the example of FIG. 1B.

With reference once again, to FIG. 1A, the source module 12 and thedestination module 14 may comprise any of a wide range of devices,including desktop computers, notebook (e.g., laptop) computers, tabletcomputers, set-top boxes, telephone handsets such as so-called “smart”phones, so-called “smart” pads, televisions, cameras, display devices,digital media players, video gaming consoles, video streaming device, orthe like. In some cases, the source module 12 and the destination module14 may be equipped for wireless communication.

The destination module 14 may receive the encoded video data to bedecoded via a link 16. The link 16 may comprise any type of medium ordevice capable of moving the encoded video data from the source module12 to the destination module 14. In the example of FIG. 1A, the link 16may comprise a communication medium to enable the source module 12 totransmit encoded video data directly to the destination module 14 inreal-time. The encoded video data may be modulated according to acommunication standard, such as a wireless communication protocol, andtransmitted to the destination module 14. The communication medium maycomprise any wireless or wired communication medium, such as a radiofrequency (RF) spectrum or one or more physical transmission lines. Thecommunication medium may form part of a packet-based network, such as alocal area network, a wide-area network, or a global network such as theInternet. The communication medium may include routers, switches, basestations, or any other equipment that may be useful to facilitatecommunication from the source module 12 to the destination module 14.

Alternatively, encoded data may be output from an output interface 22 toan optional storage device 31. Similarly, encoded data may be accessedfrom the storage device 31 by an input interface 28. The storage device31 may include any of a variety of distributed or locally accessed datastorage media such as a hard drive, flash memory, volatile ornon-volatile memory, or any other suitable digital storage media forstoring encoded video data. In a further example, the storage device 31may correspond to a file server or another intermediate storage devicethat may hold the encoded video generated by the source module 12. Thedestination module 14 may access stored video data from the storagedevice 31 via streaming or download. The file server may be any type ofserver capable of storing encoded video data and transmitting thatencoded video data to the destination module 14. Example file serversinclude a web server (e.g., for a website), an FTP server, networkattached storage (NAS) devices, or a local disk drive. The destinationmodule 14 may access the encoded video data through any standard dataconnection, including an Internet connection. This may include awireless channel (e.g., a Wi-Fi connection), a wired connection (e.g.,DSL, cable modem, etc.), or a combination of both that is suitable foraccessing encoded video data stored on a file server. The transmissionof encoded video data from the storage device 31 may be a streamingtransmission, a download transmission, or a combination of both.

The techniques of this disclosure are not limited to wirelessapplications or settings. The techniques may be applied to video codingin support of any of a variety of multimedia applications, such asover-the-air television broadcasts, cable television transmissions,satellite television transmissions, streaming video transmissions, e.g.,via the Internet (e.g., dynamic adaptive streaming over HTTP (DASH),etc.), encoding of digital video for storage on a data storage medium,decoding of digital video stored on a data storage medium, or otherapplications. In some examples, video coding system 10 may be configuredto support one-way or two-way video transmission to support applicationssuch as video streaming, video playback, video broadcasting, and/orvideo telephony.

In the example of FIG. 1A, the source module 12 includes a video source18, video encoder 20 and an output interface 22. In some cases, theoutput interface 22 may include a modulator/demodulator (modem) and/or atransmitter. In the source module 12, the video source 18 may include asource such as a video capture device, e.g., a video camera, a videoarchive containing previously captured video, a video feed interface toreceive video from a video content provider, and/or a computer graphicssystem for generating computer graphics data as the source video, or acombination of such sources. As one example, if the video source 18 is avideo camera, the source module 12 and the destination module 14 mayform so-called camera phones or video phones, as illustrated in theexample of FIG. 1B. However, the techniques described in this disclosuremay be applicable to video coding in general, and may be applied towireless and/or wired applications.

The captured, pre-captured, or computer-generated video may be encodedby the video encoder 20. The encoded video data may be transmitteddirectly to the destination module 14 via the output interface 22 of thesource module 12. The encoded video data may also (or alternatively) bestored onto the storage device 31 for later access by the destinationmodule 14 or other devices, for decoding and/or playback. The videoencoder 20 illustrated in FIGS. 1A and 1B may comprise the video encoder20 illustrated FIG. 2A, the video encoder 23 illustrated in FIG. 2B, orany other video encoder described herein.

In the example of FIG. 1A, the destination module 14 includes an inputinterface 28, a video decoder 30, and a display device 32. In somecases, the input interface 28 may include a receiver and/or a modem. Theinput interface 28 of the destination module 14 may receive the encodedvideo data over the link 16. The encoded video data communicated overthe link 16, or provided on the storage device 31, may include a varietyof syntax elements generated by the video encoder 20 for use by a videodecoder, such as the video decoder 30, in decoding the video data. Suchsyntax elements may be included with the encoded video data transmittedon a communication medium, stored on a storage medium, or stored a fileserver. The video decoder 30 illustrated in FIGS. 1A and 1B may comprisethe video decoder 30 illustrated FIG. 3A, the video decoder 33illustrated in FIG. 3B, or any other video decoder described herein.

The display device 32 may be integrated with, or external to, thedestination module 14. In some examples, the destination module 14 mayinclude an integrated display device and also be configured to interfacewith an external display device. In other examples, the destinationmodule 14 may be a display device. In general, the display device 32displays the decoded video data to a user, and may comprise any of avariety of display devices such as a liquid crystal display (LCD), aplasma display, an organic light emitting diode (OLED) display, oranother type of display device.

In related aspects, FIG. 1B shows an example video encoding and decodingsystem 10′ wherein the source and destination modules 12, 14 are on orpart of a device or user device 11. The device 11 may be a telephonehandset, such as a “smart” phone or the like. The device 11 may includean optional controller/processor module 13 in operative communicationwith the source and destination modules 12, 14. The system 10′ of FIG.1B may further include a video processing unit 21 between the videoencoder 20 and the output interface 22. In some implementations, thevideo processing unit 21 is a separate unit, as illustrated in FIG. 1B;however, in other implementations, the video processing unit 21 can beimplemented as a portion of the video encoder 20 and/or theprocessor/controller module 13. The system 10′ of FIG. 1B, andcomponents thereof, are otherwise similar to the system 10 of FIG. 1A,and components thereof.

Video encoder 20 and video decoder 30 may operate according to a videocompression standard, such as the HEVC standard presently underdevelopment, and may conform to a HEVC Test Model (HM). Alternatively,video encoder 20 and video decoder 30 may operate according to otherproprietary or industry standards, such as the ITU-T H.264 standard,alternatively referred to as MPEG-4, Part 10, Advanced Video Coding(AVC), or extensions of such standards. The techniques of thisdisclosure, however, are not limited to any particular coding standard.Other examples of video compression standards include MPEG-2 and ITU-TH.263.

Although not shown in the examples of FIGS. 1A and 1B, video encoder 20and video decoder 30 may each be integrated with an audio encoder anddecoder, and may include appropriate MUX-DEMUX units, or other hardwareand software, to handle encoding of both audio and video in a commondata stream or separate data streams. If applicable, in some examples,MUX-DEMUX units may conform to the ITU H.223 multiplexer protocol, orother protocols such as the user datagram protocol (UDP).

The video encoder 20 and the video decoder 30 each may be implemented asany of a variety of suitable encoder circuitry, such as one or moremicroprocessors, digital signal processors (DSPs), application specificintegrated circuits (ASICs), field programmable gate arrays (FPGAs),discrete logic, software, hardware, firmware or any combinationsthereof. When the techniques are implemented partially in software, adevice may store instructions for the software in a suitable,non-transitory computer-readable medium and execute the instructions inhardware using one or more processors to perform the techniques of thisdisclosure. Each of the video encoder 20 and the video decoder 30 may beincluded in one or more encoders or decoders, either of which may beintegrated as part of a combined encoder/decoder (CODEC) in a respectivedevice.

Video Coding Process

As mentioned briefly above, video encoder 20 encodes video data. Thevideo data may comprise one or more pictures. Each of the pictures is astill image forming part of a video. In some instances, a picture may bereferred to as a video “frame.” When video encoder 20 encodes the videodata, video encoder 20 may generate a bitstream. The bitstream mayinclude a sequence of bits that form a coded representation of the videodata. The bitstream may include coded pictures and associated data. Acoded picture is a coded representation of a picture.

To generate the bitstream, video encoder 20 may perform encodingoperations on each picture in the video data. When video encoder 20performs encoding operations on the pictures, video encoder 20 maygenerate a series of coded pictures and associated data. The associateddata may include a video parameter set (VPS), a sequence parameter set(SPS), a picture parameter set (PPS), an adaptation parameter set (APS),and other syntax structures. An SPS may contain parameters applicable tozero or more sequences of pictures. A PPS may contain parametersapplicable to zero or more pictures. An APS may contain parametersapplicable to zero or more pictures. Parameters in an APS may beparameters that are more likely to change than parameters in a PPS.

To generate a coded picture, video encoder 20 may partition a pictureinto equally-sized video blocks. A video block may be a two-dimensionalarray of samples. Each of the video blocks is associated with atreeblock. In some instances, a treeblock may be referred to as alargest coding unit (LCU). The treeblocks of HEVC may be broadlyanalogous to the macroblocks of previous standards, such as H.264/AVC.However, a treeblock is not necessarily limited to a particular size andmay include one or more CUs. Video encoder 20 may use quadtreepartitioning to partition the video blocks of treeblocks into videoblocks associated with CUs, hence the name “treeblocks.”

In some examples, video encoder 20 may partition a picture into aplurality of slices. Each of the slices may include an integer number ofCUs. In some instances, a slice comprises an integer number oftreeblocks. In other instances, a boundary of a slice may be within atreeblock.

As part of performing an encoding operation on a picture, video encoder20 may perform encoding operations on each slice of the picture. Whenvideo encoder 20 performs an encoding operation on a slice, videoencoder 20 may generate encoded data associated with the slice. Theencoded data associated with the slice may be referred to as a “codedslice.”

To generate a coded slice, video encoder 20 may perform encodingoperations on each treeblock in a slice. When video encoder 20 performsan encoding operation on a treeblock, video encoder 20 may generate acoded treeblock. The coded treeblock may comprise data representing anencoded version of the treeblock.

When video encoder 20 generates a coded slice, video encoder 20 mayperform encoding operations on (e.g., encode) the treeblocks in theslice according to a raster scan order. For example, video encoder 20may encode the treeblocks of the slice in an order that proceeds fromleft to right across a topmost row of treeblocks in the slice, then fromleft to right across a next lower row of treeblocks, and so on untilvideo encoder 20 has encoded each of the treeblocks in the slice.

As a result of encoding the treeblocks according to the raster scanorder, the treeblocks above and to the left of a given treeblock mayhave been encoded, but treeblocks below and to the right of the giventreeblock have not yet been encoded. Consequently, video encoder 20 maybe able to access information generated by encoding treeblocks above andto the left of the given treeblock when encoding the given treeblock.However, video encoder 20 may be unable to access information generatedby encoding treeblocks below and to the right of the given treeblockwhen encoding the given treeblock.

To generate a coded treeblock, video encoder 20 may recursively performquadtree partitioning on the video block of the treeblock to divide thevideo block into progressively smaller video blocks. Each of the smallervideo blocks may be associated with a different CU. For example, videoencoder 20 may partition the video block of a treeblock into fourequally-sized sub-blocks, partition one or more of the sub-blocks intofour equally-sized sub-sub-blocks, and so on. A partitioned CU may be aCU whose video block is partitioned into video blocks associated withother CUs. A non-partitioned CU may be a CU whose video block is notpartitioned into video blocks associated with other CUs.

One or more syntax elements in the bitstream may indicate a maximumnumber of times video encoder 20 may partition the video block of atreeblock. A video block of a CU may be square in shape. The size of thevideo block of a CU (e.g., the size of the CU) may range from 8×8 pixelsup to the size of a video block of a treeblock (e.g., the size of thetreeblock) with a maximum of 64×64 pixels or greater.

Video encoder 20 may perform encoding operations on (e.g., encode) eachCU of a treeblock according to a z-scan order. In other words, videoencoder 20 may encode a top-left CU, a top-right CU, a bottom-left CU,and then a bottom-right CU, in that order. When video encoder 20performs an encoding operation on a partitioned CU, video encoder 20 mayencode CUs associated with sub-blocks of the video block of thepartitioned CU according to the z-scan order. In other words, videoencoder 20 may encode a CU associated with a top-left sub-block, a CUassociated with a top-right sub-block, a CU associated with abottom-left sub-block, and then a CU associated with a bottom-rightsub-block, in that order.

As a result of encoding the CUs of a treeblock according to a z-scanorder, the CUs above, above-and-to-the-left, above-and-to-the-right,left, and below-and-to-the left of a given CU may have been encoded. CUsbelow and to the right of the given CU have not yet been encoded.Consequently, video encoder 20 may be able to access informationgenerated by encoding some CUs that neighbor the given CU when encodingthe given CU. However, video encoder 20 may be unable to accessinformation generated by encoding other CUs that neighbor the given CUwhen encoding the given CU.

When video encoder 20 encodes a non-partitioned CU, video encoder 20 maygenerate one or more PUs for the CU. Each of the PUs of the CU may beassociated with a different video block within the video block of theCU. Video encoder 20 may generate a predicted video block for each PU ofthe CU. The predicted video block of a PU may be a block of samples.Video encoder 20 may use intra prediction or inter prediction togenerate the predicted video block for a PU.

When video encoder 20 uses intra prediction to generate the predictedvideo block of a PU, video encoder 20 may generate the predicted videoblock of the PU based on decoded samples of the picture associated withthe PU. If video encoder 20 uses intra prediction to generate predictedvideo blocks of the PUs of a CU, the CU is an intra-predicted CU. Whenvideo encoder 20 uses inter prediction to generate the predicted videoblock of the PU, video encoder 20 may generate the predicted video blockof the PU based on decoded samples of one or more pictures other thanthe picture associated with the PU. If video encoder 20 uses interprediction to generate predicted video blocks of the PUs of a CU, the CUis an inter-predicted CU.

Furthermore, when video encoder 20 uses inter prediction to generate apredicted video block for a PU, video encoder 20 may generate motioninformation for the PU. The motion information for a PU may indicate oneor more reference blocks of the PU. Each reference block of the PU maybe a video block within a reference picture. The reference picture maybe a picture other than the picture associated with the PU. In someinstances, a reference block of a PU may also be referred to as the“reference sample” of the PU. Video encoder 20 may generate thepredicted video block for the PU based on the reference blocks of thePU.

After video encoder 20 generates predicted video blocks for one or morePUs of a CU, video encoder 20 may generate residual data for the CUbased on the predicted video blocks for the PUs of the CU. The residualdata for the CU may indicate differences between samples in thepredicted video blocks for the PUs of the CU and the original videoblock of the CU.

Furthermore, as part of performing an encoding operation on anon-partitioned CU, video encoder 20 may perform recursive quadtreepartitioning on the residual data of the CU to partition the residualdata of the CU into one or more blocks of residual data (e.g., residualvideo blocks) associated with TUs of the CU. Each TU of a CU may beassociated with a different residual video block.

Video encoder 20 may apply one or more transforms to residual videoblocks associated with the TUs to generate transform coefficient blocks(e.g., blocks of transform coefficients) associated with the TUs.Conceptually, a transform coefficient block may be a two-dimensional(2D) matrix of transform coefficients.

After generating a transform coefficient block, video encoder 20 mayperform a quantization process on the transform coefficient block.Quantization generally refers to a process in which transformcoefficients are quantized to possibly reduce the amount of data used torepresent the transform coefficients, providing further compression. Thequantization process may reduce the bit depth associated with some orall of the transform coefficients. For example, an n-bit transformcoefficient may be rounded down to an m-bit transform coefficient duringquantization, where n is greater than m.

Video encoder 20 may associate each CU with a quantization parameter(QP) value. The QP value associated with a CU may determine how videoencoder 20 quantizes transform coefficient blocks associated with theCU. Video encoder 20 may adjust the degree of quantization applied tothe transform coefficient blocks associated with a CU by adjusting theQP value associated with the CU.

After video encoder 20 quantizes a transform coefficient block, videoencoder 20 may generate sets of syntax elements that represent thetransform coefficients in the quantized transform coefficient block.Video encoder 20 may apply entropy encoding operations, such as ContextAdaptive Binary Arithmetic Coding (CABAC) operations, to some of thesesyntax elements. Other entropy coding techniques such as contentadaptive variable length coding (CAVLC), probability intervalpartitioning entropy (PIPE) coding, or other binary arithmetic codingcould also be used.

The bitstream generated by video encoder 20 may include a series ofNetwork Abstraction Layer (NAL) units. Each of the NAL units may be asyntax structure containing an indication of a type of data in the NALunit and bytes containing the data. For example, a NAL unit may containdata representing a video parameter set, a sequence parameter set, apicture parameter set, a coded slice, supplemental enhancementinformation (SEI), an access unit delimiter, filler data, or anothertype of data. The data in a NAL unit may include various syntaxstructures.

Video decoder 30 may receive the bitstream generated by video encoder20. The bitstream may include a coded representation of the video dataencoded by video encoder 20. When video decoder 30 receives thebitstream, video decoder 30 may perform a parsing operation on thebitstream. When video decoder 30 performs the parsing operation, videodecoder 30 may extract syntax elements from the bitstream. Video decoder30 may reconstruct the pictures of the video data based on the syntaxelements extracted from the bitstream. The process to reconstruct thevideo data based on the syntax elements may be generally reciprocal tothe process performed by video encoder 20 to generate the syntaxelements.

After video decoder 30 extracts the syntax elements associated with aCU, video decoder 30 may generate predicted video blocks for the PUs ofthe CU based on the syntax elements. In addition, video decoder 30 mayinverse quantize transform coefficient blocks associated with TUs of theCU. Video decoder 30 may perform inverse transforms on the transformcoefficient blocks to reconstruct residual video blocks associated withthe TUs of the CU. After generating the predicted video blocks andreconstructing the residual video blocks, video decoder 30 mayreconstruct the video block of the CU based on the predicted videoblocks and the residual video blocks. In this way, video decoder 30 mayreconstruct the video blocks of CUs based on the syntax elements in thebitstream.

Video Encoder

FIG. 2A is a block diagram illustrating an example of a video encoderthat may implement techniques in accordance with aspects described inthis disclosure. Video encoder 20 may be configured to process a singlelayer of a video frame, such as for HEVC. Further, video encoder 20 maybe configured to perform any or all of the techniques of thisdisclosure. As one example, prediction processing unit 100 may beconfigured to perform any or all of the techniques described in thisdisclosure. In another embodiment, the video encoder 20 includes anoptional inter-layer prediction unit 128 that is configured to performany or all of the techniques described in this disclosure. In otherembodiments, inter-layer prediction can be performed by predictionprocessing unit 100 (e.g., inter prediction unit 121 and/or intraprediction unit 126), in which case the inter-layer prediction unit 128may be omitted. However, aspects of this disclosure are not so limited.In some examples, the techniques described in this disclosure may beshared among the various components of video encoder 20. In someexamples, additionally or alternatively, a processor (not shown) may beconfigured to perform any or all of the techniques described in thisdisclosure.

For purposes of explanation, this disclosure describes video encoder 20in the context of HEVC coding. However, the techniques of thisdisclosure may be applicable to other coding standards or methods. Theexample depicted in FIG. 2A is for a single layer codec. However, aswill be described further with respect to FIG. 2B, some or all of thevideo encoder 20 may be duplicated for processing of a multi-layercodec.

Video encoder 20 may perform intra- and inter-coding of video blockswithin video slices. Intra coding relies on spatial prediction to reduceor remove spatial redundancy in video within a given video frame orpicture. Inter-coding relies on temporal prediction to reduce or removetemporal redundancy in video within adjacent frames or pictures of avideo sequence. Intra-mode (I mode) may refer to any of several spatialbased coding modes. Inter-modes, such as uni-directional prediction (Pmode) or bi-directional prediction (B mode), may refer to any of severaltemporal-based coding modes.

In the example of FIG. 2A, video encoder 20 includes a plurality offunctional components. The functional components of video encoder 20include a prediction processing unit 100, a residual generation unit102, a transform processing unit 104, a quantization unit 106, aninverse quantization unit 108, an inverse transform unit 110, areconstruction unit 112, a filter unit 113, a decoded picture buffer114, and an entropy encoding unit 116. Prediction processing unit 100includes an inter prediction unit 121, a motion estimation unit 122, amotion compensation unit 124, an intra prediction unit 126, and aninter-layer prediction unit 128. In other examples, video encoder 20 mayinclude more, fewer, or different functional components. Furthermore,motion estimation unit 122 and motion compensation unit 124 may behighly integrated, but are represented in the example of FIG. 2Aseparately for purposes of explanation.

Video encoder 20 may receive video data. Video encoder 20 may receivethe video data from various sources. For example, video encoder 20 mayreceive the video data from video source 18 (e.g., shown in FIG. 1A or1B) or another source. The video data may represent a series ofpictures. To encode the video data, video encoder 20 may perform anencoding operation on each of the pictures. As part of performing theencoding operation on a picture, video encoder 20 may perform encodingoperations on each slice of the picture. As part of performing anencoding operation on a slice, video encoder 20 may perform encodingoperations on treeblocks in the slice.

As part of performing an encoding operation on a treeblock, predictionprocessing unit 100 may perform quadtree partitioning on the video blockof the treeblock to divide the video block into progressively smallervideo blocks. Each of the smaller video blocks may be associated with adifferent CU. For example, prediction processing unit 100 may partitiona video block of a treeblock into four equally-sized sub-blocks,partition one or more of the sub-blocks into four equally-sizedsub-sub-blocks, and so on.

The sizes of the video blocks associated with CUs may range from 8×8samples up to the size of the treeblock with a maximum of 64×64 samplesor greater. In this disclosure, “N×N” and “N by N” may be usedinterchangeably to refer to the sample dimensions of a video block interms of vertical and horizontal dimensions, e.g., 16×16 samples or 16by 16 samples. In general, a 16×16 video block has sixteen samples in avertical direction (y=16) and sixteen samples in a horizontal direction(x=16). Likewise, an N×N block generally has N samples in a verticaldirection and N samples in a horizontal direction, where N represents anonnegative integer value.

Furthermore, as part of performing the encoding operation on atreeblock, prediction processing unit 100 may generate a hierarchicalquadtree data structure for the treeblock. For example, a treeblock maycorrespond to a root node of the quadtree data structure. If predictionprocessing unit 100 partitions the video block of the treeblock intofour sub-blocks, the root node has four child nodes in the quadtree datastructure. Each of the child nodes corresponds to a CU associated withone of the sub-blocks. If prediction processing unit 100 partitions oneof the sub-blocks into four sub-sub-blocks, the node corresponding tothe CU associated with the sub-block may have four child nodes, each ofwhich corresponds to a CU associated with one of the sub-sub-blocks.

Each node of the quadtree data structure may contain syntax data (e.g.,syntax elements) for the corresponding treeblock or CU. For example, anode in the quadtree may include a split flag that indicates whether thevideo block of the CU corresponding to the node is partitioned (e.g.,split) into four sub-blocks. Syntax elements for a CU may be definedrecursively, and may depend on whether the video block of the CU issplit into sub-blocks. A CU whose video block is not partitioned maycorrespond to a leaf node in the quadtree data structure. A codedtreeblock may include data based on the quadtree data structure for acorresponding treeblock.

Video encoder 20 may perform encoding operations on each non-partitionedCU of a treeblock. When video encoder 20 performs an encoding operationon a non-partitioned CU, video encoder 20 generates data representing anencoded representation of the non-partitioned CU.

As part of performing an encoding operation on a CU, predictionprocessing unit 100 may partition the video block of the CU among one ormore PUs of the CU. Video encoder 20 and video decoder 30 may supportvarious PU sizes. Assuming that the size of a particular CU is 2N×2N,video encoder 20 and video decoder 30 may support PU sizes of 2N×2N orN×N, and inter-prediction in symmetric PU sizes of 2N×2N, 2N×N, N×2N,N×N, 2N×nU, nL×2N, nR×2N, or similar. Video encoder 20 and video decoder30 may also support asymmetric partitioning for PU sizes of 2N×nU,2N×nD, nL×2N, and nR×2N. In some examples, prediction processing unit100 may perform geometric partitioning to partition the video block of aCU among PUs of the CU along a boundary that does not meet the sides ofthe video block of the CU at right angles.

Inter prediction unit 121 may perform inter prediction on each PU of theCU. Inter prediction may provide temporal compression. To perform interprediction on a PU, motion estimation unit 122 may generate motioninformation for the PU. Motion compensation unit 124 may generate apredicted video block for the PU based the motion information anddecoded samples of pictures other than the picture associated with theCU (e.g., reference pictures). In this disclosure, a predicted videoblock generated by motion compensation unit 124 may be referred to as aninter-predicted video block.

Slices may be I slices, P slices, or B slices. Motion estimation unit122 and motion compensation unit 124 may perform different operationsfor a PU of a CU depending on whether the PU is in an I slice, a Pslice, or a B slice. In an I slice, all PUs are intra predicted. Hence,if the PU is in an I slice, motion estimation unit 122 and motioncompensation unit 124 do not perform inter prediction on the PU.

If the PU is in a P slice, the picture containing the PU is associatedwith a list of reference pictures referred to as “list 0.” Each of thereference pictures in list 0 contains samples that may be used for interprediction of other pictures. When motion estimation unit 122 performsthe motion estimation operation with regard to a PU in a P slice, motionestimation unit 122 may search the reference pictures in list 0 for areference block for the PU. The reference block of the PU may be a setof samples, e.g., a block of samples, that most closely corresponds tothe samples in the video block of the PU. Motion estimation unit 122 mayuse a variety of metrics to determine how closely a set of samples in areference picture corresponds to the samples in the video block of a PU.For example, motion estimation unit 122 may determine how closely a setof samples in a reference picture corresponds to the samples in thevideo block of a PU by sum of absolute difference (SAD), sum of squaredifference (SSD), or other difference metrics.

After identifying a reference block of a PU in a P slice, motionestimation unit 122 may generate a reference index that indicates thereference picture in list 0 containing the reference block and a motionvector that indicates a spatial displacement between the PU and thereference block. In various examples, motion estimation unit 122 maygenerate motion vectors to varying degrees of precision. For example,motion estimation unit 122 may generate motion vectors at one-quartersample precision, one-eighth sample precision, or other fractionalsample precision. In the case of fractional sample precision, referenceblock values may be interpolated from integer-position sample values inthe reference picture. Motion estimation unit 122 may output thereference index and the motion vector as the motion information of thePU. Motion compensation unit 124 may generate a predicted video block ofthe PU based on the reference block identified by the motion informationof the PU.

If the PU is in a B slice, the picture containing the PU may beassociated with two lists of reference pictures, referred to as “list 0”and “list 1.” In some examples, a picture containing a B slice may beassociated with a list combination that is a combination of list 0 andlist 1.

Furthermore, if the PU is in a B slice, motion estimation unit 122 mayperform uni-directional prediction or bi-directional prediction for thePU. When motion estimation unit 122 performs uni-directional predictionfor the PU, motion estimation unit 122 may search the reference picturesof list 0 or list 1 for a reference block for the PU. Motion estimationunit 122 may then generate a reference index that indicates thereference picture in list 0 or list 1 that contains the reference blockand a motion vector that indicates a spatial displacement between the PUand the reference block. Motion estimation unit 122 may output thereference index, a prediction direction indicator, and the motion vectoras the motion information of the PU. The prediction direction indicatormay indicate whether the reference index indicates a reference picturein list 0 or list 1. Motion compensation unit 124 may generate thepredicted video block of the PU based on the reference block indicatedby the motion information of the PU.

When motion estimation unit 122 performs bi-directional prediction for aPU, motion estimation unit 122 may search the reference pictures in list0 for a reference block for the PU and may also search the referencepictures in list 1 for another reference block for the PU. Motionestimation unit 122 may then generate reference indexes that indicatethe reference pictures in list 0 and list 1 containing the referenceblocks and motion vectors that indicate spatial displacements betweenthe reference blocks and the PU. Motion estimation unit 122 may outputthe reference indexes and the motion vectors of the PU as the motioninformation of the PU. Motion compensation unit 124 may generate thepredicted video block of the PU based on the reference blocks indicatedby the motion information of the PU.

In some instances, motion estimation unit 122 does not output a full setof motion information for a PU to entropy encoding unit 116. Rather,motion estimation unit 122 may signal the motion information of a PUwith reference to the motion information of another PU. For example,motion estimation unit 122 may determine that the motion information ofthe PU is sufficiently similar to the motion information of aneighboring PU. In this example, motion estimation unit 122 mayindicate, in a syntax structure associated with the PU, a value thatindicates to video decoder 30 that the PU has the same motioninformation as the neighboring PU. In another example, motion estimationunit 122 may identify, in a syntax structure associated with the PU, aneighboring PU and a motion vector difference (MVD). The motion vectordifference indicates a difference between the motion vector of the PUand the motion vector of the indicated neighboring PU. Video decoder 30may use the motion vector of the indicated neighboring PU and the motionvector difference to determine the motion vector of the PU. By referringto the motion information of a first PU when signaling the motioninformation of a second PU, video encoder 20 may be able to signal themotion information of the second PU using fewer bits.

As part of performing an encoding operation on a CU, intra predictionunit 126 may perform intra prediction on PUs of the CU. Intra predictionmay provide spatial compression. When intra prediction unit 126 performsintra prediction on a PU, intra prediction unit 126 may generateprediction data for the PU based on decoded samples of other PUs in thesame picture. The prediction data for the PU may include a predictedvideo block and various syntax elements. Intra prediction unit 126 mayperform intra prediction on PUs in I slices, P slices, and B slices.

To perform intra prediction on a PU, intra prediction unit 126 may usemultiple intra prediction modes to generate multiple sets of predictiondata for the PU. When intra prediction unit 126 uses an intra predictionmode to generate a set of prediction data for the PU, intra predictionunit 126 may extend samples from video blocks of neighboring PUs acrossthe video block of the PU in a direction and/or gradient associated withthe intra prediction mode. The neighboring PUs may be above, above andto the right, above and to the left, or to the left of the PU, assuminga left-to-right, top-to-bottom encoding order for PUs, CUs, andtreeblocks. Intra prediction unit 126 may use various numbers of intraprediction modes, e.g., 33 directional intra prediction modes, dependingon the size of the PU.

Prediction processing unit 100 may select the prediction data for a PUfrom among the prediction data generated by motion compensation unit 124for the PU or the prediction data generated by intra prediction unit 126for the PU. In some examples, prediction processing unit 100 selects theprediction data for the PU based on rate/distortion metrics of the setsof prediction data.

If prediction processing unit 100 selects prediction data generated byintra prediction unit 126, prediction processing unit 100 may signal theintra prediction mode that was used to generate the prediction data forthe PUs, e.g., the selected intra prediction mode. Prediction processingunit 100 may signal the selected intra prediction mode in various ways.For example, it is probable the selected intra prediction mode is thesame as the intra prediction mode of a neighboring PU. In other words,the intra prediction mode of the neighboring PU may be the most probablemode for the current PU. Thus, prediction processing unit 100 maygenerate a syntax element to indicate that the selected intra predictionmode is the same as the intra prediction mode of the neighboring PU.

As discussed above, the video encoder 20 may include inter-layerprediction unit 128. Inter-layer prediction unit 128 is configured topredict a current block (e.g., a current block in the EL) using one ormore different layers that are available in SVC (e.g., a base orreference layer). Such prediction may be referred to as inter-layerprediction. Inter-layer prediction unit 128 utilizes prediction methodsto reduce inter-layer redundancy, thereby improving coding efficiencyand reducing computational resource requirements. Some examples ofinter-layer prediction include inter-layer intra prediction, inter-layermotion prediction, and inter-layer residual prediction. Inter-layerintra prediction uses the reconstruction of co-located blocks in thebase layer to predict the current block in the enhancement layer.Inter-layer motion prediction uses motion information of the base layerto predict motion in the enhancement layer. Inter-layer residualprediction uses the residue of the base layer to predict the residue ofthe enhancement layer. Each of the inter-layer prediction schemes isdiscussed below in greater detail.

After prediction processing unit 100 selects the prediction data for PUsof a CU, residual generation unit 102 may generate residual data for theCU by subtracting (e.g., indicated by the minus sign) the predictedvideo blocks of the PUs of the CU from the video block of the CU. Theresidual data of a CU may include 2D residual video blocks thatcorrespond to different sample components of the samples in the videoblock of the CU. For example, the residual data may include a residualvideo block that corresponds to differences between luminance componentsof samples in the predicted video blocks of the PUs of the CU andluminance components of samples in the original video block of the CU.In addition, the residual data of the CU may include residual videoblocks that correspond to the differences between chrominance componentsof samples in the predicted video blocks of the PUs of the CU and thechrominance components of the samples in the original video block of theCU.

Prediction processing unit 100 may perform quadtree partitioning topartition the residual video blocks of a CU into sub-blocks. Eachundivided residual video block may be associated with a different TU ofthe CU. The sizes and positions of the residual video blocks associatedwith TUs of a CU may or may not be based on the sizes and positions ofvideo blocks associated with the PUs of the CU. A quadtree structureknown as a “residual quad tree” (RQT) may include nodes associated witheach of the residual video blocks. The TUs of a CU may correspond toleaf nodes of the RQT.

Transform processing unit 104 may generate one or more transformcoefficient blocks for each TU of a CU by applying one or moretransforms to a residual video block associated with the TU. Each of thetransform coefficient blocks may be a 2D matrix of transformcoefficients. Transform processing unit 104 may apply various transformsto the residual video block associated with a TU. For example, transformprocessing unit 104 may apply a discrete cosine transform (DCT), adirectional transform, or a conceptually similar transform to theresidual video block associated with a TU.

After transform processing unit 104 generates a transform coefficientblock associated with a TU, quantization unit 106 may quantize thetransform coefficients in the transform coefficient block. Quantizationunit 106 may quantize a transform coefficient block associated with a TUof a CU based on a QP value associated with the CU.

Video encoder 20 may associate a QP value with a CU in various ways. Forexample, video encoder 20 may perform a rate-distortion analysis on atreeblock associated with the CU. In the rate-distortion analysis, videoencoder 20 may generate multiple coded representations of the treeblockby performing an encoding operation multiple times on the treeblock.Video encoder 20 may associate different QP values with the CU whenvideo encoder 20 generates different encoded representations of thetreeblock. Video encoder 20 may signal that a given QP value isassociated with the CU when the given QP value is associated with the CUin a coded representation of the treeblock that has a lowest bitrate anddistortion metric.

Inverse quantization unit 108 and inverse transform unit 110 may applyinverse quantization and inverse transforms to the transform coefficientblock, respectively, to reconstruct a residual video block from thetransform coefficient block. Reconstruction unit 112 may add thereconstructed residual video block to corresponding samples from one ormore predicted video blocks generated by prediction processing unit 100to produce a reconstructed video block associated with a TU. Byreconstructing video blocks for each TU of a CU in this way, videoencoder 20 may reconstruct the video block of the CU.

After reconstruction unit 112 reconstructs the video block of a CU,filter unit 113 may perform a deblocking operation to reduce blockingartifacts in the video block associated with the CU. After performingthe one or more deblocking operations, filter unit 113 may store thereconstructed video block of the CU in decoded picture buffer 114.Motion estimation unit 122 and motion compensation unit 124 may use areference picture that contains the reconstructed video block to performinter prediction on PUs of subsequent pictures. In addition, intraprediction unit 126 may use reconstructed video blocks in decodedpicture buffer 114 to perform intra prediction on other PUs in the samepicture as the CU.

Entropy encoding unit 116 may receive data from other functionalcomponents of video encoder 20. For example, entropy encoding unit 116may receive transform coefficient blocks from quantization unit 106 andmay receive syntax elements from prediction processing unit 100. Whenentropy encoding unit 116 receives the data, entropy encoding unit 116may perform one or more entropy encoding operations to generate entropyencoded data. For example, video encoder 20 may perform a contextadaptive variable length coding (CAVLC) operation, a CABAC operation, avariable-to-variable (V2V) length coding operation, a syntax-basedcontext-adaptive binary arithmetic coding (SBAC) operation, aProbability Interval Partitioning Entropy (PIPE) coding operation, oranother type of entropy encoding operation on the data. Entropy encodingunit 116 may output a bitstream that includes the entropy encoded data.

As part of performing an entropy encoding operation on data, entropyencoding unit 116 may select a context model. If entropy encoding unit116 is performing a CABAC operation, the context model may indicateestimates of probabilities of particular bins having particular values.In the context of CABAC, the term “bin” is used to refer to a bit of abinarized version of a syntax element.

Multi-Layer Video Encoder

FIG. 2B is a block diagram illustrating an example of a multi-layervideo encoder 23 that may implement techniques in accordance withaspects described in this disclosure. The video encoder 23 may beconfigured to process multi-layer video frames, such as for SHVC andmultiview coding. Further, the video encoder 23 may be configured toperform any or all of the techniques of this disclosure.

The video encoder 23 includes a video encoder 20A and video encoder 20B,each of which may be configured as the video encoder 20 and may performthe functions described above with respect to the video encoder 20.Further, as indicated by the reuse of reference numbers, the videoencoders 20A and 20B may include at least some of the systems andsubsystems as the video encoder 20. Although the video encoder 23 isillustrated as including two video encoders 20A and 20B, the videoencoder 23 is not limited as such and may include any number of videoencoder 20 layers. In some embodiments, the video encoder 23 may includea video encoder 20 for each picture or frame in an access unit. Forexample, an access unit that includes five pictures may be processed orencoded by a video encoder that includes five encoder layers. In someembodiments, the video encoder 23 may include more encoder layers thanframes in an access unit. In some such cases, some of the video encoderlayers may be inactive when processing some access units.

In addition to the video encoders 20A and 20B, the video encoder 23 mayinclude a resampling unit 90. The resampling unit 90 may, in some cases,upsample a base layer of a received video frame to, for example, createan enhancement layer. The resampling unit 90 may upsample particularinformation associated with the received base layer of a frame, but notother information. For example, the resampling unit 90 may up sample thespatial size or number of pixels of the base layer, but the number ofslices or the picture order count may remain constant. In some cases,the resampling unit 90 may not process the received video and/or may beoptional. For example, in some cases, the prediction processing unit 100may perform upsampling. In some embodiments, the resampling unit 90 isconfigured to upsample a layer and reorganize, redefine, modify, oradjust one or more slices to comply with a set of slice boundary rulesand/or raster scan rules. Although primarily described as upsampling abase layer, or a lower layer in an access unit, in some cases, theresampling unit 90 may downsample a layer. For example, if duringstreaming of a video bandwidth is reduced, a frame may be downsampledinstead of upsampled.

The resampling unit 90 may be configured to receive a picture or frame(or picture information associated with the picture) from the decodedpicture buffer 114 of the lower layer encoder (e.g., the video encoder20A) and to upsample the picture (or the received picture information).This upsampled picture may then be provided to the prediction processingunit 100 of a higher layer encoder (e.g., the video encoder 20B)configured to encode a picture in the same access unit as the lowerlayer encoder. In some cases, the higher layer encoder is one layerremoved from the lower layer encoder. In other cases, there may be oneor more higher layer encoders between the layer 0 video encoder and thelayer 1 encoder of FIG. 2B.

In some cases, the resampling unit 90 may be omitted or bypassed. Insuch cases, the picture from the decoded picture buffer 114 of the videoencoder 20A may be provided directly, or at least without being providedto the resampling unit 90, to the prediction processing unit 100 of thevideo encoder 20B. For example, if video data provided to the videoencoder 20B and the reference picture from the decoded picture buffer114 of the video encoder 20A are of the same size or resolution, thereference picture may be provided to the video encoder 20B without anyresampling.

In some embodiments, the video encoder 23 downsamples video data to beprovided to the lower layer encoder using the downsampling unit 94before provided the video data to the video encoder 20A. Alternatively,the downsampling unit 94 may be a resampling unit 90 capable ofupsampling or downsampling the video data. In yet other embodiments, thedownsampling unit 94 may be omitted.

As illustrated in FIG. 2B, the video encoder 23 may further include amultiplexor 98, or mux. The mux 98 can output a combined bitstream fromthe video encoder 23. The combined bitstream may be created by taking abitstream from each of the video encoders 20A and 20B and alternatingwhich bitstream is output at a given time. While in some cases the bitsfrom the two (or more in the case of more than two video encoder layers)bitstreams may be alternated one bit at a time, in many cases thebitstreams are combined differently. For example, the output bitstreammay be created by alternating the selected bitstream one block at atime. In another example, the output bitstream may be created byoutputting a non-1:1 ratio of blocks from each of the video encoders 20Aand 20B. For instance, two blocks may be output from the video encoder20B for each block output from the video encoder 20A. In someembodiments, the output stream from the mux 98 may be preprogrammed. Inother embodiments, the mux 98 may combine the bitstreams from the videoencoders 20A, 20B based on a control signal received from a systemexternal to the video encoder 23, such as from a processor on a sourcedevice including the source module 12. The control signal may begenerated based on the resolution or bitrate of a video from the videosource 18, based on a bandwidth of the link 16, based on a subscriptionassociated with a user (e.g., a paid subscription versus a freesubscription), or based on any other factor for determining a resolutionoutput desired from the video encoder 23.

Video Decoder

FIG. 3A is a block diagram illustrating an example of a video decoderthat may implement techniques in accordance with aspects described inthis disclosure. The video decoder 30 may be configured to process asingle layer of a video frame, such as for HEVC. Further, video decoder30 may be configured to perform any or all of the techniques of thisdisclosure. As one example, motion compensation unit 162 and/or intraprediction unit 164 may be configured to perform any or all of thetechniques described in this disclosure. In one embodiment, videodecoder 30 may optionally include inter-layer prediction unit 166 thatis configured to perform any or all of the techniques described in thisdisclosure. In other embodiments, inter-layer prediction can beperformed by prediction processing unit 152 (e.g., motion compensationunit 162 and/or intra prediction unit 164), in which case theinter-layer prediction unit 166 may be omitted. However, aspects of thisdisclosure are not so limited. In some examples, the techniquesdescribed in this disclosure may be shared among the various componentsof video decoder 30. In some examples, additionally or alternatively, aprocessor (not shown) may be configured to perform any or all of thetechniques described in this disclosure.

For purposes of explanation, this disclosure describes video decoder 30in the context of HEVC coding. However, the techniques of thisdisclosure may be applicable to other coding standards or methods. Theexample depicted in FIG. 3A is for a single layer codec. However, aswill be described further with respect to FIG. 3B, some or all of thevideo decoder 30 may be duplicated for processing of a multi-layercodec.

In the example of FIG. 3A, video decoder 30 includes a plurality offunctional components. The functional components of video decoder 30include an entropy decoding unit 150, a prediction processing unit 152,an inverse quantization unit 154, an inverse transform unit 156, areconstruction unit 158, a filter unit 159, and a decoded picture buffer160. Prediction processing unit 152 includes a motion compensation unit162, an intra prediction unit 164, and an inter-layer prediction unit166. In some examples, video decoder 30 may perform a decoding passgenerally reciprocal to the encoding pass described with respect tovideo encoder 20 of FIG. 2A. In other examples, video decoder 30 mayinclude more, fewer, or different functional components.

Video decoder 30 may receive a bitstream that comprises encoded videodata. The bitstream may include a plurality of syntax elements. Whenvideo decoder 30 receives the bitstream, entropy decoding unit 150 mayperform a parsing operation on the bitstream. As a result of performingthe parsing operation on the bitstream, entropy decoding unit 150 mayextract syntax elements from the bitstream. As part of performing theparsing operation, entropy decoding unit 150 may entropy decode entropyencoded syntax elements in the bitstream. Prediction processing unit152, inverse quantization unit 154, inverse transform unit 156,reconstruction unit 158, and filter unit 159 may perform areconstruction operation that generates decoded video data based on thesyntax elements extracted from the bitstream.

As discussed above, the bitstream may comprise a series of NAL units.The NAL units of the bitstream may include video parameter set NALunits, sequence parameter set NAL units, picture parameter set NALunits, SEI NAL units, and so on. As part of performing the parsingoperation on the bitstream, entropy decoding unit 150 may performparsing operations that extract and entropy decode sequence parametersets from sequence parameter set NAL units, picture parameter sets frompicture parameter set NAL units, SEI data from SEI NAL units, and so on.

In addition, the NAL units of the bitstream may include coded slice NALunits. As part of performing the parsing operation on the bitstream,entropy decoding unit 150 may perform parsing operations that extractand entropy decode coded slices from the coded slice NAL units. Each ofthe coded slices may include a slice header and slice data. The sliceheader may contain syntax elements pertaining to a slice. The syntaxelements in the slice header may include a syntax element thatidentifies a picture parameter set associated with a picture thatcontains the slice. Entropy decoding unit 150 may perform entropydecoding operations, such as CABAC decoding operations, on syntaxelements in the coded slice header to recover the slice header.

As part of extracting the slice data from coded slice NAL units, entropydecoding unit 150 may perform parsing operations that extract syntaxelements from coded CUs in the slice data. The extracted syntax elementsmay include syntax elements associated with transform coefficientblocks. Entropy decoding unit 150 may then perform CABAC decodingoperations on some of the syntax elements.

After entropy decoding unit 150 performs a parsing operation on anon-partitioned CU, video decoder 30 may perform a reconstructionoperation on the non-partitioned CU. To perform the reconstructionoperation on a non-partitioned CU, video decoder 30 may perform areconstruction operation on each TU of the CU. By performing thereconstruction operation for each TU of the CU, video decoder 30 mayreconstruct a residual video block associated with the CU.

As part of performing a reconstruction operation on a TU, inversequantization unit 154 may inverse quantize, e.g., de-quantize, atransform coefficient block associated with the TU. Inverse quantizationunit 154 may inverse quantize the transform coefficient block in amanner similar to the inverse quantization processes proposed for HEVCor defined by the H.264 decoding standard. Inverse quantization unit 154may use a quantization parameter QP calculated by video encoder 20 for aCU of the transform coefficient block to determine a degree ofquantization and, likewise, a degree of inverse quantization for inversequantization unit 154 to apply.

After inverse quantization unit 154 inverse quantizes a transformcoefficient block, inverse transform unit 156 may generate a residualvideo block for the TU associated with the transform coefficient block.Inverse transform unit 156 may apply an inverse transform to thetransform coefficient block in order to generate the residual videoblock for the TU. For example, inverse transform unit 156 may apply aninverse DCT, an inverse integer transform, an inverse Karhunen-Loevetransform (KLT), an inverse rotational transform, an inverse directionaltransform, or another inverse transform to the transform coefficientblock. In some examples, inverse transform unit 156 may determine aninverse transform to apply to the transform coefficient block based onsignaling from video encoder 20. In such examples, inverse transformunit 156 may determine the inverse transform based on a signaledtransform at the root node of a quadtree for a treeblock associated withthe transform coefficient block. In other examples, inverse transformunit 156 may infer the inverse transform from one or more codingcharacteristics, such as block size, coding mode, or the like. In someexamples, inverse transform unit 156 may apply a cascaded inversetransform.

In some examples, motion compensation unit 162 may refine the predictedvideo block of a PU by performing interpolation based on interpolationfilters. Identifiers for interpolation filters to be used for motioncompensation with sub-sample precision may be included in the syntaxelements. Motion compensation unit 162 may use the same interpolationfilters used by video encoder 20 during generation of the predictedvideo block of the PU to calculate interpolated values for sub-integersamples of a reference block. Motion compensation unit 162 may determinethe interpolation filters used by video encoder 20 according to receivedsyntax information and use the interpolation filters to produce thepredicted video block.

If a PU is encoded using intra prediction, intra prediction unit 164 mayperform intra prediction to generate a predicted video block for the PU.For example, intra prediction unit 164 may determine an intra predictionmode for the PU based on syntax elements in the bitstream. The bitstreammay include syntax elements that intra prediction unit 164 may use todetermine the intra prediction mode of the PU.

In some instances, the syntax elements may indicate that intraprediction unit 164 is to use the intra prediction mode of another PU todetermine the intra prediction mode of the current PU. For example, itmay be probable that the intra prediction mode of the current PU is thesame as the intra prediction mode of a neighboring PU. In other words,the intra prediction mode of the neighboring PU may be the most probablemode for the current PU. Hence, in this example, the bitstream mayinclude a small syntax element that indicates that the intra predictionmode of the PU is the same as the intra prediction mode of theneighboring PU. Intra prediction unit 164 may then use the intraprediction mode to generate prediction data (e.g., predicted samples)for the PU based on the video blocks of spatially neighboring PUs.

As discussed above, video decoder 30 may also include inter-layerprediction unit 166. Inter-layer prediction unit 166 is configured topredict a current block (e.g., a current block in the EL) using one ormore different layers that are available in SVC (e.g., a base orreference layer). Such prediction may be referred to as inter-layerprediction. Inter-layer prediction unit 166 utilizes prediction methodsto reduce inter-layer redundancy, thereby improving coding efficiencyand reducing computational resource requirements. Some examples ofinter-layer prediction include inter-layer intra prediction, inter-layermotion prediction, and inter-layer residual prediction. Inter-layerintra prediction uses the reconstruction of co-located blocks in thebase layer to predict the current block in the enhancement layer.Inter-layer motion prediction uses motion information of the base layerto predict motion in the enhancement layer. Inter-layer residualprediction uses the residue of the base layer to predict the residue ofthe enhancement layer. Each of the inter-layer prediction schemes isdiscussed below in greater detail.

Reconstruction unit 158 may use the residual video blocks associatedwith TUs of a CU and the predicted video blocks of the PUs of the CU,e.g., either intra-prediction data or inter-prediction data, asapplicable, to reconstruct the video block of the CU. Thus, videodecoder 30 may generate a predicted video block and a residual videoblock based on syntax elements in the bitstream and may generate a videoblock based on the predicted video block and the residual video block.

After reconstruction unit 158 reconstructs the video block of the CU,filter unit 159 may perform a deblocking operation to reduce blockingartifacts associated with the CU. After filter unit 159 performs adeblocking operation to reduce blocking artifacts associated with theCU, video decoder 30 may store the video block of the CU in decodedpicture buffer 160. Decoded picture buffer 160 may provide referencepictures for subsequent motion compensation, intra prediction, andpresentation on a display device, such as display device 32 of FIG. 1Aor 1B. For instance, video decoder 30 may perform, based on the videoblocks in decoded picture buffer 160, intra prediction or interprediction operations on PUs of other CUs.

Multi-Layer Decoder

FIG. 3B is a block diagram illustrating an example of a multi-layervideo decoder 33 that may implement techniques in accordance withaspects described in this disclosure. The video decoder 33 may beconfigured to process multi-layer video frames, such as for SHVC andmultiview coding. Further, the video decoder 33 may be configured toperform any or all of the techniques of this disclosure.

The video decoder 33 includes a video decoder 30A and video decoder 30B,each of which may be configured as the video decoder 30 and may performthe functions described above with respect to the video decoder 30.Further, as indicated by the reuse of reference numbers, the videodecoders 30A and 30B may include at least some of the systems andsubsystems as the video decoder 30. Although the video decoder 33 isillustrated as including two video decoders 30A and 30B, the videodecoder 33 is not limited as such and may include any number of videodecoder 30 layers. In some embodiments, the video decoder 33 may includea video decoder 30 for each picture or frame in an access unit. Forexample, an access unit that includes five pictures may be processed ordecoded by a video decoder that includes five decoder layers. In someembodiments, the video decoder 33 may include more decoder layers thanframes in an access unit. In some such cases, some of the video decoderlayers may be inactive when processing some access units.

In addition to the video decoders 30A and 30B, the video decoder 33 mayinclude an upsampling unit 92. In some embodiments, the upsampling unit92 may upsample a base layer of a received video frame to create anenhanced layer to be added to the reference picture list for the frameor access unit. This enhanced layer can be stored in the decoded picturebuffer 160. In some embodiments, the upsampling unit 92 can include someor all of the embodiments described with respect to the resampling unit90 of FIG. 2A. In some embodiments, the upsampling unit 92 is configuredto upsample a layer and reorganize, redefine, modify, or adjust one ormore slices to comply with a set of slice boundary rules and/or rasterscan rules. In some cases, the upsampling unit 92 may be a resamplingunit configured to upsample and/or downsample a layer of a receivedvideo frame

The upsampling unit 92 may be configured to receive a picture or frame(or picture information associated with the picture) from the decodedpicture buffer 160 of the lower layer decoder (e.g., the video decoder30A) and to upsample the picture (or the received picture information).This upsampled picture may then be provided to the prediction processingunit 152 of a higher layer decoder (e.g., the video decoder 30B)configured to decode a picture in the same access unit as the lowerlayer decoder. In some cases, the higher layer decoder is one layerremoved from the lower layer decoder. In other cases, there may be oneor more higher layer decoders between the layer 0 decoder and the layer1 decoder of FIG. 3B.

In some cases, the upsampling unit 92 may be omitted or bypassed. Insuch cases, the picture from the decoded picture buffer 160 of the videodecoder 30A may be provided directly, or at least without being providedto the upsampling unit 92, to the prediction processing unit 152 of thevideo decoder 30B. For example, if video data provided to the videodecoder 30B and the reference picture from the decoded picture buffer160 of the video decoder 30A are of the same size or resolution, thereference picture may be provided to the video decoder 30B withoutupsampling. Further, in some embodiments, the upsampling unit 92 may bea resampling unit 90 configured to upsample or downsample a referencepicture received from the decoded picture buffer 160 of the videodecoder 30A.

As illustrated in FIG. 3B, the video decoder 33 may further include ademultiplexor 99, or demux. The demux 99 can split an encoded videobitstream into multiple bitstreams with each bitstream output by thedemux 99 being provided to a different video decoder 30A and 30B. Themultiple bitstreams may be created by receiving a bitstream and each ofthe video decoders 30A and 30B receives a portion of the bitstream at agiven time. While in some cases the bits from the bitstream received atthe demux 99 may be alternated one bit at a time between each of thevideo decoders (e.g., video decoders 30A and 30B in the example of FIG.3B), in many cases the bitstream is divided differently. For example,the bitstream may be divided by alternating which video decoder receivesthe bitstream one block at a time. In another example, the bitstream maybe divided by a non-1:1 ratio of blocks to each of the video decoders30A and 30B. For instance, two blocks may be provided to the videodecoder 30B for each block provided to the video decoder 30A. In someembodiments, the division of the bitstream by the demux 99 may bepreprogrammed. In other embodiments, the demux 99 may divide thebitstream based on a control signal received from a system external tothe video decoder 33, such as from a processor on a destination deviceincluding the destination module 14. The control signal may be generatedbased on the resolution or bitrate of a video from the input interface28, based on a bandwidth of the link 16, based on a subscriptionassociated with a user (e.g., a paid subscription versus a freesubscription), or based on any other factor for determining a resolutionobtainable by the video decoder 33.

Intra Random Access Point (IRAP) Pictures

Some video coding schemes may provide various random access pointsthroughout the bitstream such that the bitstream may be decoded startingfrom any of those random access points without needing to decode anypictures that precede those random access points in the bitstream. Insuch video coding schemes, all pictures that follow a random accesspoint in output order (e.g., including those pictures that are in thesame access unit as the picture providing the random access point) canbe correctly decoded without using any pictures that precede the randomaccess point. For example, even if a portion of the bitstream is lostduring transmission or during decoding, a decoder can resume decodingthe bitstream starting from the next random access point. Support forrandom access may facilitate, for example, dynamic streaming services,seek operations, channel switching, etc.

In some coding schemes, such random access points may be provided bypictures that are referred to as intra random access point (IRAP)pictures. For example, a random access point (e.g., provided by anenhancement layer IRAP picture) in an enhancement layer (“layerA”)contained in an access unit (“auA”) may provide layer-specific randomaccess such that for each reference layer (“layerB”) of layerA (e.g., areference layer being a layer that is used to predict layerA) having arandom access point contained in an access unit (“auB”) that is inlayerB and precedes auA in decoding order (or a random access pointcontained in auA), the pictures in layerA that follow auB in outputorder (including those pictures located in auB), are correctly decodablewithout needing to decode any pictures in layerA that precede auB.

IRAP pictures may be coded using intra prediction (e.g., coded withoutreferring to other pictures) and/or inter-layer prediction, and mayinclude, for example, instantaneous decoder refresh (IDR) pictures,clean random access (CRA) pictures, and broken link access (BLA)pictures. When there is an IDR picture in the bitstream, all thepictures that precede the IDR picture in decoding order are not used forprediction by pictures that follow the IDR picture. When there is a CRApicture in the bitstream, the pictures that follow the CRA picture mayor may not use pictures that precede the CRA picture in decoding orderfor prediction. Those pictures that follow the CRA picture in decodingorder but use pictures that precede the CRA picture in decoding ordermay be referred to as random access skipped leading (RASL) pictures.Another type of picture that can follow an IRAP picture in decodingorder and precede it in output order is a random access decodableleading (RADL) picture, which may not contain references to any picturesthat precede the IRAP picture in decoding order. RASL pictures may bediscarded by the decoder if the pictures that precede the CRA pictureare not available. A BLA picture indicates to the decoder that picturesthat precede the BLA picture may not be available to the decoder (e.g.,because two bitstreams are spliced together and the BLA picture is thefirst picture of the second bitstream in decoding order). An access unit(e.g., a group of pictures consisting of all the coded picturesassociated with the same output time across multiple layers) containinga base layer picture (e.g., having a layer ID of 0) that is an IRAPpicture may be referred to as an IRAP access unit. The layer ID of alayer, such as the base layer, may be contained in a nuh_layer_id value.In some aspects, the base layer may have a layer ID of 0.

Direct Dependency Flag

In some example implementations (e.g., MV-HEVC and SHVC), there is asyntax element called direct_dependency_flag that specifies, for aparticular layer, which layer or layers can be used for inter-layerprediction of the particular layer. In one embodiment, thedirect_dependency_flag is a two-dimensional array that specifies whetherone layer of video data is coded based on (or dependent on) anotherlayer of video data. Such a two-dimensional array may take a form ofvalues direct_dependency_flag[i][j], where i corresponds to the layer tobe coded (e.g., current layer) and j corresponds to the layer to bereferenced (e.g., reference layer). In this example,direct_dependency_flag may be 0 if the reference layer is not a directreference layer of the current layer, and direct_dependency_flag may be1 if the reference layer is a direct reference layer of the currentlayer. In one embodiment, if direct_dependency_flag is omitted orundefined, the value is inferred to be 0. In another embodiment, ifdirect_dependency_flag is omitted or undefined, the value is inferred tobe 1. In one embodiment, if Layer A is a direct reference layer of LayerB, it means that Layer B can be coded based at least in part oninformation included in Layer A. In another embodiment, if Layer A is adirect reference layer of Layer B, it means that Layer B is coded basedat least in part on information included in Layer A. In someembodiments, all the layers that have a smaller layer ID (e.g., lowerlayer) are direct reference layers of a particular layer. In otherembodiments, only some of the lower layers may be direct referencelayers of a particular layer. For example, the encoder may choose onlysome of the lower layers as direct dependency layers of a particularlayer to reduce computational complexity. The applicable coding scheme(e.g., HEVC) may have a limit as to how many direct reference layers aparticular layer may have (e.g., no more than one reference layer forspatial scalability). In one embodiment, the direct_dependency_flag_flagis signaled in the video parameter set (VPS) and applies to the entirecoded video sequence (CVS).

Direct Dependency Type

The information that is used to code the current layer may includetexture information (e.g., pixel values) of the reference layer, motioninformation (e.g., motion vectors, reference indices, predictiondirection, etc.) of the reference layer. However, the information of thereference layer that may be used to code the current layer is notlimited to those discussed herein, but can be any information that isincluded in or part of the reference layer.

In some implementations, one or more additional flags or syntax elementsmay be used to indicate the type or types of information that arederived or imported from the reference layer to code the current layer.For example, in some embodiments, the reference layer may be used forinter-layer motion prediction, inter-layer texture prediction, or both.In one embodiment, such a flag or syntax element may be called“direct_dependency_type.”

In one embodiment, the direct_dependency_type is a two-dimensional arraythat specifies which type of inter-layer prediction is used for codingthe current layer using the reference layer. Such a two-dimensionalarray may take a form of values direct_dependency_type[i][j], where icorresponds to the current (e.g., layer to be coded) and j correspondsto the reference layer (e.g., layer to be referenced). In this example,a direct_dependency_type value of 0 may indicate inter-layer sampleprediction only, 1 may indicate inter-layer motion prediction only, and2 may indicate both inter-layer sample and motion prediction. In someembodiments, a direct_dependency_type value of 3 (or any other value)may indicate that there is no dependency. How eachdirect_dependency_type value is assigned or mapped to different types ofinter-layer prediction may be different in other implementations, andthe present disclosure is not limited to any particular assignment ormapping of direct_dependency_type values to different types ofinter-layer prediction. In one embodiment, the direct_dependency_typesyntax element is signaled in the video parameter set (VPS) and appliesto the entire coded video sequence (CVS).

Reference Layer Codec

In some existing coding schemes, a reference or base layer codec may beany number of codecs. For example, an HEVC codec may be used for thereference layer or an H.264/AVC may be used, or a general, non-HEVCcodec. In addition, there may be a flag in a parameter set indicatingthe codec to be used. For example, a flag in the video parameter set(VPS) may indicate whether HEVC or non-HEVC (e.g., AVC) codec is used tocode the reference layer. In one example, a flag avc_base_layer_flag mayhave a value equal to 1, indicating that the reference layer codecconforms to the video coding standard according to Recommendation ITU-TH.264|International Standard ISO/IEC 14496-10, and alternatively, mayhave a value equal to 0, indicating that the reference layer codecconforms to the HEVC specification. Therefore, a coding deviceconfigured to encode or decode an enhancement layer may have informationregarding whether an AVC or HEVC codec (or some other non-HEVC codec) isused with respect to the reference layer.

For example, in some aspects, a non-HEVC codec may be used for areference or base layer, and one or more enhancement layers may be basedon an H.265/HEVC coding standards and its multi-layer extensions. Forexample, these enhancement layers may be based the Scalable extension ofH.265/HEVC (SHVC). Using such a configuration may have a number ofadvantages. For example, this may allow devices which are compatibleonly with non-HEVC codecs to decode the video without the enhancementlayers, and further allow devices that are compatible with HEVC codecsto decode the video and the enhancement layers.

Support for SHVC-Based Enhancement Layers

Certain designs may allow for support of a H.264/AVC (or other non-HEVC)base layer, with SHVC-based enhancement layers. Accordingly, two or moredecoders may be used to decode a video using these techniques. Forexample, one decoder may decode the non-HEVC base layer as is known inthe art. Another decoder, such as an HEVC decoder, may be used to decodethe one or more SHVC-based enhancement layers. In some aspects, it maybe beneficial to provide a design for the enhancement layers which mayallow the HEVC decoder to decode these layers when a non-HEVC base layeris used. From the point of view of the HEVC decoder, these base layersmay be decoded by an external source or an external means. Accordingly,the HEVC decoder may not receive any information from the base layer, ormay only receive a limited subset of information from the base layer,such as the image information for each frame from the base layer.

When decoding an HEVC-based enhancement layer in a video that includes anon-HEVC-based base layer, no base layer picture information may beprovided to the enhancement layer. Alternatively, the external source(such as a base layer decoder) may provide a proscribed set ofinformation to the decoder, including the decoded sample values of thebase layer decoded picture, the representation format of the base layerdecoded picture, including the width and height in luma samples, thecolor format, the luma bit depth, and the chroma bit depth, and anindication whether the base layer picture is an IDR picture or not.Optionally, information also be provided on whether the picture is aframe or a field, and when a field, the field parity (indicating whetherthe field is a top field or a bottom field). If this information is notprovided, the decoded picture may be inferred to be a frame picture.

Outputting a base layer picture may be the responsibility of a baselayer decoder. For example, this decoder may be an H.264/AVC decoder, ora decoder of another non-HEVC codec. Output synchronization between thebase layer picture and an enhancement layer picture in the same accessunit may be externally controlled. For example, one method of externalcontrol may be to use presentation timestamps. In some aspects, theassociation of a base layer decoded picture to an access unit may be theresponsibility of the external source/source, such as the base layerdecoder or another source that is external to the enhancement layerdecoder.

In some aspects, an SHVC decoder, which is used to decode one or moreenhancement layer, may only need to keep one decoded picture store ofmemory for a base layer decoded picture, and this memory may notconsidered as part of the decoded picture buffer (DPB).

The non-HEVC base layer decoded picture may have a layer ID(nuh_layer_id value) of 0. In some aspects, a HevcBaseLayerFlag valuemay be used to indicate whether or not the base layer is an HEVC baselayer. When the base layer is not an HEVC base layer, this flag may havea value of 0, while this flag may have a value of 1 when the base layeris an HEVC layer.

In some aspects, the picture order count of the base layer decodedpicture is set equal to the picture order count of the enhancement layerpictures. Note that in this case the actual picture order count of abase layer picture decoded by the base layer decoder in such a scalableor multiview codec might be different than the picture order count valueof the same picture when it is decoded by an AVC decoder.

In some aspects, the base layer decoded picture may be marked as “usedfor long-term reference.” For the coded picture buffer operations of thehypothetical reference decoder or buffering model, the base layer may beconsidered as having zero bits. For decoded picture buffer operations ofthe hypothetical reference decoder or buffering model, only decodedpictures of enhancement layers may be considered.

Identified Issues with Support for SHVC-Based Enhancement Layers

As described above, SHVC-based enhancement layers may be used with abase layer that used a non-HEVC codec, such as an H.264/AVC codec.However, these SHVC-based enhancement layers may encounter certainproblems, due to the combination of the SHVC-based enhancement layersand the non-HEVC base layer. Certain issues may not arise when using anHEVC base layer, but only when using a non-HEVC base layer, such as whena decoded picture is provided to the SHVC coder by an external source,such as an AVC coder.

In some aspects, when the base layer is a non-HEVC layer, signaling ofcertain parameters may be done in a manner which limits the amount ofbits used for such signaling. For example, it may be advantageous to usea limited amount of bits for certain DPB parameters, such as those whichassign a sub-DPB size, a maximum reorder and a maximum latency. Further,it may be advantageous if certain syntax structures do not apply to thebase layer (layer 0) when the base layer is a non-HVEC layer.

For example, signaling of certain parameters may be unnecessary orredundant when using a non-HEVC base layer. Certain parameters may beinferred simply from the presence of the non-HEVC base layer, and thus,any further signaling of those parameters may be unnecessary. Thus, inorder to efficiently use memory and other resources, a coder may beconfigured to determine whether or not a base layer is coded using anHEVC codec, and to choose whether or not to signal certain parametersbased, at least in part, on the codec used for a base layer of a videostream. When the base layer is a non-HEVC base layer, a coder may beconfigured to infer certain values of these parameters, rather than havethose values explicitly defined.

In some aspects, a base layer decoded picture may be provided by theexternal means or external source. It may be advantageous if thispicture is stored in a sub-DPB for the base layer. The size of thissub-DPB may be set to 1, and the sub-DPB may be emptied at the end ofthe decoding process for each access unit.

It may also be advantageous if the base layer decoder (which may bereferred to as an external source, because it is external to theSHVC-decoder) provides certain values to the SHVC-decoder, which containinformation about the base layer. For example, the external source mayprovide a decoded base layer picture, and may also provide an indicationof whether or not the base layer picture is an IRAP picture. If the baselayer picture is an IRAP picture, the external source may be furtherrequired to provide the coder with an IRAP NAL unit type, whichspecifies whether the picture is an IDR picture, a CRA picture, or a BLApicture.

Efficient Signaling of DPB Parameters

In some aspects, certain signaling of DPB parameters may be inefficientwhen using a non-HEVC base layer and one or more SVHC-based enhancementlayer. For example, certain parameters may have constrained values whena base layer is a non-HEVC base layer. For example, a given parametermay have a single, particular value whenever the base layer is anon-HEVC layer. Accordingly, signaling these values for each element inan array (or other data structure) may be redundant, as these values maybe inferred based upon an indicating that the base layer is a non-HEVClayer, or inferred base upon other information.

For example, one DPB parameter that may be signaled isvps_max_dec_pic_buffering_minus1[i]. The value of this array, plus 1,signals the maximum required size of the decoded picture buffer for thehighest temporal sub-layer to be decoded. However, when using a non-HEVCbase layer, vps_max_dec_pic_buffering_minus1[i] will be for all possiblevalues of i. Accordingly, since the value ofvps_max_dec_pic_buffering_minus1[i] is constrained when using a non-HEVCbase layer, it may be desirable to avoid signaling these values.

For example, when a non-HEVC base layer is present, the value ofHevcBaseLayerFlag may be set to 0, and the value of AvcBaseLayerFlag maybe set to 1. Accordingly, the coder may be configured to check one ormore of these values prior to setting a value forvps_max_dec_pic_buffering_minus1[i]. When the coder determines that anon-HEVC base layer is present, the coder may then refrain from settingvalues for vps_max_dec_pic_buffering_minus1[i] for each value of i, asthis value may be inferred from other information, such as an indicationthat the base layer is coded using a non-HEVC codec.

In some aspects, the coder may be configured to set each value ofvps_max_dec_pic_buffering_minus1[i] to 0, for each possible i, when thecoder determines that a non-HEVC base layer is present. For example,this value or another value may use the least amount of bits possible tosignal vps_max_dec_pic_buffering_minus1[i]. It may be beneficial to usethe least amount of bits possible to signal values ofvps_max_dec_pic_buffering_minus1[i], when values of the array areconstrained due to the use of a non-HEVC base layer. Accordingly, valuesfor vps_max_dec_pic_buffering_minus1[i] may be set to 0 for all valuesof i. When decoding, a decoder may be configured to ignore these valuesas the values may be constrained based upon the use of the non-HEVC baselayer.

Further, the vps_sub_layer_ordering_info_present_flag may be present andset to when a non-HEVC base layer is used. A value of 1 may indicatethat vps_max_dec_pic_buffering_minus1[i], vps_max_num_reorder_pics[i],and vps_max_latency_increase_plus1[i] are present for the i sublayers,while a value of 0 may indicate that values ofvps_max_dec_pic_buffering_minus1[vps_max_sub_layers_minus1],vps_max_num_reorder_pics[vps_max_sub_layers_minus1], andvps_max_latency_increase_plus1[vps_max_sub_layers_minus1] apply to allsub-layers (such that each of these arrays has the same value for eachof the i sublayers).

Another DPB parameter that may be signaled isvps_max_num_reorder_pics[i], which indicates a maximum amount ofreordering that can occur between pictures to be outputted. For example,certain pictures that are to be outputted may precede another picture tobe outputted in the coding order, but may follow that same picture inthe output order. The maximum reordering value(vps_max_num_reorder_pics[i]) indicates, for a value of HighestTid equalto i, a maximum allowed number of pictures that are set to be outputtedwhich may proceed a given output picture in the decoding order, butfollow that same picture in the output order.

As with vps_max_dec_pic_buffering_minus1[i], when the base layer is anon-HEVC layer, vps_max_num_reorder_pics[i] may be set to 0 for allvalues of i. Accordingly, it may be advantageous for the coder to notsignal the values of vps_max_num_reorder_pics[i], after the coder hasdetermined that the base layer is a non-HEVC base layer. When this valueis not signaled, values of vps_max_num_reorder_pics[i] may be inferred,based upon an indication that the base layer is a non-HEVC layer. Insome aspects, the coder may be configured to set each value ofvps_max_num_reorder_pics[i] to 0, for each possible i, when the coderdetermines that a non-HEVC base layer is present.

In some aspects, the coder may be configured to set each value ofvps_max_num_reorder_pics[i] to 0, for each possible i, when the coderdetermines that a non-HEVC base layer is present. For example, thisvalue or another value may use the least amount of bits possible tosignal vps_max_num_reorder_pics[i]. It may be beneficial to use theleast amount of bits possible to signal values ofvps_max_num_reorder_pics[i], when values of the array are constraineddue to the use of a non-HEVC base layer. Accordingly, values forvps_max_num_reorder_pics[i] may be set to 0 for all values of i. Whendecoding, a decoder may be configured to ignore these values as thevalues may be constrained based upon the use of the non-HEVC base layer.

Another DPB parameter that may be signaled isvps_max_latency_increase_plus1[i]. A value of this parameter not equalto 0 may be used to compute a maximum number of output pictures that canprecede an output picture with in the video stream in output order andfollow that output picture in decoding order when the highest temporalsub-layer to be decoded is equal to i.

As above, when the base layer is a non-HEVC layer,vps_max_latency_increase_plus1[i] may be set to 0 for all values of i.Accordingly, it may be advantageous for the coder to not signal thevalues of vps_max_latency_increase_plus1[i], after the coder hasdetermined that the base layer is a non-HEVC base layer. When this valueis not signaled, values of vps_max_latency_increase_plus1[i] may beinferred, based upon an indication that the base layer is a non-HEVClayer. In some aspects, the coder may be configured to set each value ofvps_max_latency_increase_plus1[i] to 0, for each possible i, when thecoder determines that a non-HEVC base layer is present.

In some aspects, the coder may be configured to set each value ofvps_max_latency_increase_plus1 [i] to 0, for each possible i, when thecoder determines that a non-HEVC base layer is present. For example,this value or another value may use the least amount of bits possible tosignal vps_max_latency_increase_plus1 [i]. It may be beneficial to usethe least amount of bits possible to signal values ofvps_max_latency_increase_plus1 [i], when values of the array areconstrained due to the use of a non-HEVC base layer. Accordingly, valuesfor vps_max_latency_increase_plus1 [i] may be set to 0 for all values ofi. When decoding, a decoder may be configured to ignore these values asthe values may be constrained based upon the use of the non-HEVC baselayer.

Accordingly, as described above, it may be advantageous for a coder touse the least amount of bits possible to signalvps_max_dec_pic_buffering_minus1[i], vps_max_num_reorder_pics[i], andvps_max_latency_increase_plus1 [i]. For example, if the values of eachof these arrays are constrained when a non-HEVC base layer is used, itmay be advantageous to signal these values using fewer bits than wouldbe needed in situations where the values are not constrained. Forexample, the values for each of these arrays may be set to 0 for allvalues of i. A decoder may then be configured to ignore these values.For example, a decoder may be configured to determine whether or not abase layer is an HEVC base layer, such as by checking a flag. If thebase layer is a non-HEVC base layer, the decoder may be configured toignore the values of each of vps_max_dec_pic_buffering_minus1[i],vps_max_num_reorder_pics[i], and vps_max_latency_increase_plus1 [i].

In some aspects, hrd_layer_set_idx[i] may be used to specify the layerset to which the i-th hrd_parameters( ) syntax structure in the VPSapplies. In previous versions of video streams, it may have beenspecified that hrd_layer_set_idx[i] may be equal to 0. Accordingly, itmay be beneficial for hrd_layer_set_idx[i] to be greater than 0, suchthat a decoder may be aware that the video stream is a video streamwhich has a non-HEVC base layer, rather than adhering to priorstandards. Further, in some aspects, none of the hrd_parameters( )syntax structures may apply to the non-HEVC base layer, which has alayer ID of 0. For example, when the base layer is signaled to benon-HEVC or externally-provided, there should be no HRD parametersapplicable to the base layer, as the base layer is not in the bitstream.

Example Flowchart #1

FIG. 4 is a flowchart illustrating a method 400 for coding videoinformation, according to an embodiment of the present disclosure. Thesteps illustrated in FIG. 4 may be performed by an encoder (e.g., thevideo encoder as shown in FIG. 2A or FIG. 2B), a decoder (e.g., thevideo decoder as shown in FIG. 3A or FIG. 3B), or any other component.For convenience, method 400 is described as performed by a coder, whichmay be the encoder, the decoder, or another component. The method may bea method of decoding, or a method of encoding.

The method 400 begins at block 401. In block 405, the coder determineswhether a reference layer is included in a bitstream. For example, thereference layer may not be included in the bitstream when the referencelayer is a non-HEVC codec. Accordingly, in some aspects, the referencelayer may be coded in a non-HEVC codec, or may be coded in an AVC codec,and therefore may not be included in the bitstream. In some aspects, themethod determines whether the reference layer is included in thebitstream based upon a value of a flag or a variable. Such a flag orother indicator may be received from the external source, or may bedetermined by the method. In some aspects, the means for determining mayinclude a processor.

Next, at block 410, the coder determines an indication of one or moreparameters for a decoded picture buffer based upon whether the referencelayer is included in the bitstream. For example the one or moreparameters for a decoded picture buffer may include a parameter whichsignals the maximum required size of the DPB, such as a maximum size ofa sub-DPB. Generally, if the reference layer is not included in thebitstream, the values for the these parameters may be known, asdescribed above. In some aspects, determining an indication for themaximum size of the sub-DPB may include determining an indication forthe maximum size of the sub-DPB which indicates that the maximum size ofthe sub-DPB is 1. In some aspects, the means for determining may includea processor. In the video encoding process, the coder may include one ormore syntax structures into the bitstream that include the indication ofthe one or more parameters. In the video decoding process, determiningthe indication may include decoding one or more syntax structures fromthe bitstream. Details of example syntax structures are describedherein.

In some aspects, the parameter may also include a value which signals amaximum number of reordering of output pictures, or a maximum latency.In some aspects, certain parameters may be determined based, at least inpart, on the codec used for the base layer. For example, in someaspects, the values of one or more parameters may be set to 0, for allpossible values of i, when the base layer is a non-HVEC codec. At block415, the coder codes the video information based at least in part on thedetermined indication of the one or more parameters for the decodedpicture buffer. In some aspects, the means for coding may include aprocessor. The method 400 ends at block 425.

As discussed above, one or more components of video encoder 20 of FIG.2A, video encoder 21 of FIG. 2B, video decoder 30 of FIG. 3A, or videodecoder 31 of FIG. 3B (e.g., inter-layer prediction unit 128 and/orinter-layer prediction unit 166) may be used to implement any of thetechniques discussed in the present disclosure, such as determiningwhether the reference layer codec is the particular type of codec,receiving the decoded base layer picture, storing the decoded base layerpicture, and emptying the memory.

Reducing Unnecessary Signaling in the VPS Extension when Using aNon-HEVC Base Layer

In some aspects, when the base layer is a non-HEVC base layer, it may bedesirable to avoid unnecessary signalling for the base layer in the VPSextension, including VPS video usability information (VUI) metadata. Forexample, the VPS VUI may include a number of values that may be inferredsimply based on the knowledge that the base layer is encoded using anon-HEVC codec, and thus, it may be unnecessary to continue to signalthis redundant information in the video.

For example, certain values in the VPS VUI may be determined solelybased on the knowledge that the base layer is a non-HEVC base layer.Accordingly, if it is signaled that the base layer is a non-HEVC baselayer, further signaling on certain values in the VPS VUI may beredundant and unnecessary. As described above, if the value of aHevcBaseLayerFlag is set to 0, this may signal that the base layer isnot an HEVC layer. Accordingly, other signaling may be avoided asredundant and unnecessary.

As described above, direct_dependency_type[i][j] indicates a type ofdependency between the layer i and layer j. For example, a value of 0indicates that layer j may be used for both inter-layer sampleprediction and inter-layer motion prediction for layer i. A value of 1indicates that layer j may be used for inter-layer sample prediction butnot for inter-layer motion prediction for layer i. A value of 2indicates that layer j may be used for inter-layer motion prediction butnot for inter-layer sample prediction for layer i.

When using a base layer that is non-HEVC, inter-layer motion predictionfrom the base layer may be disallowed for all other layers. As describedabove the non-HEVC base layer has a layer ID of 0. Further, wheninter-layer motion prediction is not allowed, this may correspond with adirect_dependency_type value of 1. Thus, the value ofdirect_dependency_type[i][0] may be inferred to be 1 for all values ofi, because no layer may use the base layer (with layer ID of 0) forinter-layer motion prediction. These values need not be explicitlysignaled, as such signaling may be redundant after an indication thatthe base layer is a non-HEVC base layer.

For example, a coder, either an encoder or a decoder, may recognize thatthe base layer is a non-HEVC base layer. Based upon this recognition(which may be recognized, for example, based upon one or more indicationsuch as a flag), the coder may be configured to infer values ofdirect_dependency_type[i][0] for all values of i, such that the inferredvalues may be 1 for all values of i.

In some aspects, the following code segment may be used to avoidunnecessary signaling in the VPS extension. This code segment may avoidsignaling values for direct_dependency_type[i][0] since, as describedabove, those values may be inferred based upon the indication that thebase layer is not an HEVC layer:

vps_extension( ) { Descriptor ...  if( default_direct_dependency_flag )  default_direct_dependency_type u(v)  else {   for( i =HevcBaseLayerFlag ? 1 : 2; i <=   MaxLayersMinus1; i++ )    for( j =HevcBaseLayerFlag ? 0 : 1; j < i; j++ )     if( direct_dependency_flag[i ][ j ] )       direct_dependency_type[ i ][ j ] u(v)  }

Other values in the VPS VUI may also be unnecessary or redundant afterit has been signaled that the base layer is a non-HEVC layer. Forexample, the value of sub_layers_vps_max_minus1[0] may also be inferredbased on the presence of a non-HEVC base layer.

For example, sub_layers_vps_max_minus1[i] plus 1 specifies the maximumnumber of temporal sub-layers that may be present in the coded videosequence for layer i. As before, the layer ID of the base layer is 0.Because the base layer is decoded by external source and not by thedecoder (that is, the SHVC decoder), the base layer will not contain anysub-layers, and so it is unnecessary to signal a value forsub_layers_vps_max_minus1[0] for a non-HEVC base layer. Accordingly, acoder may be configured to infer this value based upon recognizing thatthe base layer is a non-HEVC base layer.

In some aspects, the following code segment from vps_extension( ) may beused to avoid signaling the value of sub_layers_vps_max_minus1[0], whenthe base layer is a non-HEVC base layer, since this value may beunnecessary:

vps_extension( ) { Descriptor ... vps_sub_layers_max_minus1_present_flag u(1)   if( vps_sub_layers_(—)max_minus1_present_flag )    for( i = HevcBaseLayerFlag ? 0 : 1; i <=   MaxLayersMinus1; i++ )     sub_layers_vps_max_minus1[ i ] u(3)

Other values in the VPS VUI may also be unnecessary or redundant afterit has been signaled that the base layer is a non-HEVC layer. Forexample, the value of max_tid_il_ref_pics_plus1[0][j] may also beinferred based on the presence of a non-HEVC base layer.

Generally, max_tid_il_ref_pics_plus1[i][j] may be used to determinewhether or not a picture from layer i, with a given TemporalId, may beused for inter-layer prediction for a picture from layer j. A valueequal to 0 indicates that non-IRAP pictures from layer i are not usedfor inter-layer prediction with layer j. A value greater than 0indicates that pictures from layer i with TemporalId less than or equalto max_tid_il_ref_pics_plus1[i][j] may be used as reference forinter-layer prediction for pictures from layer j. When not present,max_tid_il_ref_pics_plus1[i][j] is inferred to be equal to 7.

However, when the base layer is a non-HEVC base layer and not present inthe bitstream, the value of max_tid_il_ref_pics_plus1 [0][j] (where thebase layer is layer 0) that indicates whether or not a picture fromlayer 0, with a given TemporalId, may be used for inter-layer predictionfor a picture from layer j becomes less useful. Thus, explicit signalingof this value may be unnecessary, and may be avoided.

In some aspects, the following code segment may be used invps_extension( ) in order to avoid signaling values formax_tid_il_ref_pics_plus1[0][j] when the base layer is a non-HEVC baselayer:

vps_extension( ) { Descriptor ...  max_tid_ref_present_flag u(1)  if(max_tid_ref_present_flag )   for( i = HevcBaseLayerFlag ? 0 : 1; i <  MaxLayersMinus1; i++ )    for( j = i + 1; j <= MaxLayersMinus1; j++ )    if( direct_dependency_flag[ j ][ i ] )      max_tid_il_ref_pics_plus1[ i ][ j ] u(3)

Example Flowchart #2

FIG. 5 is a flowchart illustrating a method 500 for coding videoinformation, according to an embodiment of the present disclosure. Thesteps illustrated in FIG. 5 may be performed by an encoder (e.g., thevideo encoder as shown in FIG. 2A or FIG. 2B), a decoder (e.g., thevideo decoder as shown in FIG. 3A or FIG. 3B), or any other component.For convenience, method 500 is described as performed by a coder, whichmay be the encoder, the decoder, or another component. The method may bea method of decoding, or a method of encoding.

The method 500 begins at block 501. In block 505, the coder determineswhether a reference layer is in a bitstream. In one embodiment, thereference layer may be coded using an AVC codec and/or a non-HEVC codec.In some aspects, the coder, or the processor determines whether thereference layer is included in the bitstream based upon a value of aflag or other indicator of the codec. Such a flag or other indicator maybe received from the external source, or may be determined by themethod. In some aspects, the means for determining may include aprocessor. In the video encoding process, the determining whether thereference layer is included in the bitstream based upon a value of aflag or other indicator of the codec may include generating one or moresyntax structures into the bitstream. In the video decoding process, thedetermining whether the reference layer is included in the bitstreambased upon a value of a flag or other indicator of the codec may includedecoding one or more syntax structures from the bitstream. Details ofexample syntax structures are described herein.

Next, the coder determines whether or not to process an indication forthe reference layer, based on whether the reference layer is included inthe bitstream, at block 510. For example, this determination may bebased on whether or not the indication would be rendered redundant orunnecessary, based upon whether the reference layer is included in thebitstream. For example, certain indications may have a known value whena reference layer is not included in a bitstream, such that signalingthe indication may be unnecessary. In some aspects, the indication mayinclude an indication of a type of inter-layer prediction that a givenlayer may be used for, such as motion prediction and sample prediction.In some aspects, the indication may be an indication of a number ofsub-layers for a particular layer, which may be unnecessary to signalfor a base layer that is being coded by external source. In someaspects, the indication may be an indication of whether or not a givenlayer may be used for inter-layer prediction for another layer. In someaspects, the means for determining may include a processor.

At block 515, the coder processes, in a video bitstream, and indicationfor the reference layer if the reference layer is included in thebitstream. For example, certain indications may be processed only whenthe reference layer is included in the bitstream, such as when thereference layer is coded using an HEVC codec. In other situations, theseindications may not be processed, as they may be unnecessary orredundant. In some aspects, the means for determining may include aprocessor.

At block 520, the coder codes the video information based at least inpart on the processed indication. In some aspects, the means for codingmay include a processor. The method 500 ends at block 525.

As discussed above, one or more components of video encoder 20 of FIG.2A, video encoder 21 of FIG. 2B, video decoder 30 of FIG. 3A, or videodecoder 31 of FIG. 3B (e.g., inter-layer prediction unit 128 and/orinter-layer prediction unit 166) may be used to implement any of thetechniques discussed in the present disclosure, such as determiningwhether the reference layer codec is the particular type of codec,receiving the decoded base layer picture, storing the decoded base layerpicture, and emptying the memory.

Storing Decoded Base Layer Pictures in the DPB

In some aspects, the decoded base layer picture provided by externalsource (such as a base layer decoder) for an access unit is not storedin the DPB, yet it is marked as “used for long-term reference” and lateron used for inter-layer prediction reference. Accordingly, this may beproblematic, as such a decoded picture may not be used for reference,such as for inter-layer prediction reference, unless it is in the DPB.

Because the base layer (layer ID 0) in the video stream is a non-HEVClayer, the decoder may not receive a coded picture in layer 0. Asbefore, the decoder here refers to the SHVC decoder, which may be usedto decode one or more enhancement layers. Rather, the base layer may bedecoded using external source. These external sources may include, forexample, an AVC decoder which is configured to decode the base layer andto pass the decoded base layer picture to the SHVC decoder. In additionto the decoded base layer picture, the external source may be configuredto provide certain other information to the decoder as well, asdescribed above.

Accordingly, the base layer may contain a decoded picture, with layer IDof 0. The decoder may be configured to store the decoded base layerpicture in the sub-DPB, and to mark this picture as “used for long-termreference.” Further, if an access unit has at least one picture with alayer ID greater than 0, the PicOrderCntVal of the base layer decodedpicture is set to be equal to the PicOrderCntVal of any other picture inthe access unit. Otherwise, the base layer picture is discarded and thesub-DPB for the base layer is set to be empty, if there are no otherpictures in the access unit aside from the base layer decoded picture.

When the access unit has at least one picture with a layer ID greaterthan 0, after all the pictures in the access unit are decoded, thesub-DPB for the base layer is set to be empty. That is, the sub-DPBwhich contains the decoded base layer picture may be emptied after eachpicture in the access unit has been decoded. The size of the sub-DPB maybe set equal to 1. Thus, the sub-DPB may store one picture, and eachaccess unit may include one base layer decoded picture.

Example Flowchart #3

FIG. 6 is a flowchart illustrating a method 600 for decoding videoinformation, according to an embodiment of the present disclosure. Thesteps illustrated in FIG. 6 may be performed by a decoder (e.g., thevideo decoder as shown in FIG. 3A or FIG. 3B), or any other component.In some aspects, the method determines whether the reference layer isincluded in the bitstream based upon a value of a flag or a variable,such as a value included in a one of a video parameter set, a sequenceparameter set, a picture parameter set, or an adaptation parameter set.Such a flag or other indicator may be received from the external source,or may be determined by the method. In some aspects, the means fordetermining may include a processor.

The method 600 begins at block 601. In block 605, the decoder determinesthat a reference layer is not included in a bitstream. In one example,the reference layer may be coded according to an AVC codec and/or anon-HEVC codec. In some aspects, the method determines whether thebitstream includes a reference layer based upon a value of a flag orother indicator of the codec. The value may be included in a one of avideo parameter set, a sequence parameter set, a picture parameter set,or an adaptation parameter set. Such a flag or other indicator may bereceived from the external source, or may be determined by the method.In some aspects, the means for determining may include a processor.

Next, the decoder receives a decoded base layer picture from an externalsource, the decoded base layer picture associated with an access unit,in block 610. In one aspect, the external source may include anotherdecoder, such as a decoder which is configured to use an AVC codec, or adecoder which is configured to use a non-HEVC codec. For example, theexternal source may include a second decoder. In some aspects, there mayone decoded base layer picture associated with each access unit. In someaspects, the means for determining may include a processor.

The decoder then stores the decoded base layer picture in a memory inblock 615. The memory may include a DPB or a sub-DPB. In some aspects,the sub-DPB may be sized such that it can hold one, and only one,decoded base layer picture. In some aspects, the decoder may furtherprovide an indication that the decoded base layer picture may be usedfor long-term reference. In some aspects, the means for storing mayinclude a memory.

The decoder then decodes pictures associated with the access unit basedon the stored decoded base layer picture in block 618. The means fordecoding may include a processor. The coder, subsequent to decoding thepictures associated with the access unit, empties the decoded base layerpicture from the memory in block 620. In some aspects, the means foremptying may include a processor. The method 600 ends at block 625.

As discussed above, one or more components of video encoder 20 of FIG.2A, video encoder 21 of FIG. 2B, video decoder 30 of FIG. 3A, or videodecoder 31 of FIG. 3B (e.g., inter-layer prediction unit 128 and/orinter-layer prediction unit 166) may be used to implement any of thetechniques discussed in the present disclosure, such as determiningwhether the reference layer codec is the particular type of codec,receiving the decoded base layer picture, storing the decoded base layerpicture, and emptying the memory.

Signaling an IRAP Base Layer Picture

In some aspects, it may be beneficial for a decoder, such as an SHVCdecoder operating on one or more enhancement layers, to be aware ofcertain properties of the non-HVEC base layer. For example, it may bedesirable for the decoder to require that the external source signalwhether a given base layer picture is an IRAP picture or not. If thebase layer picture is an IRAP picture, it may be desirable if theexternal source further signals the IRAP NAL unit type, which mayspecify and IDR picture, a CRA picture, or a BLA picture.

When a non-HEVC base layer is used, each access unit may include adecoded base layer picture (with layer ID equal to 0) by an externalsource. When such a picture is not provided, no base layer picture maybe used for inter-layer prediction for that access unit.

When a decoded base layer picture is provided by the external source,the external source may also provide other information. For example, theexternal source may provide decoded sample values. If the valuechroma_format_idc is equal to 0, the external source may provide onesample array S_(L) as a decoded sample value. Otherwise, the externalsource may provide 3 sample arrays, S_(L), S_(Cb), and S_(Cr).

The external source may also provide an indication of whether or not thedecoded base layer picture is an IRAP picture. For example, thisindication may be found in a variable named BlIrapPicFlag. This baselayer IRAP picture flag may indicate whether or not the base layerpicture is an IRAP picture. A value of 1 may indicate that the baselayer picture is an IRAP picture. Similarly, if a variable namedIrapPicFlag is equal to 1, this may indicate that the decoded base layerpicture is a non-IRAP picture.

When the base layer picture is an IRAP picture, the external source mayfurther provide the IRAP NAL unit type. This may specify an IDR picture,a CRA picture, or a BLA picture. For example, this may be provided as avalue for a variable nal_unit_type. This variable may have a value ofIDR_W_RADL, CRA_NUT, or BLA_W_LP, which may indicate if the IRAP pictureis an IDR picture, a CRA picture, or a BLA picture, respectively.

For example, the NAL unit type variable may indicate that the IRAP baselayer picture is IDR_W_RADL. This value may indicate that decodedpicture is an IDR picture and was decoded from a Rec. ITU-TH.264|ISO/IEC 14496-10 IDR picture.

In some aspects, the NAL unit type variable may indicate that the IRAPbase layer picture is CRA_NUT. This specifies that the decoded pictureis a CRA picture and was decoded from a Rec. ITU-T H.264|ISO/IEC14496-10 coded picture that was associated with a Rec. ITU-TH.264|ISO/IEC 14496-10 recovery point SEI message withrecovery_frame_cnt equal to 0 and broken_link_flag equal to 0.

In some aspects, the NAL unit type variable may indicate that the IRAPbase layer picture is BLA_W_LP. This specifies that the decoded pictureis a BLA picture and was decoded from a Rec. ITU-T H.264|ISO/IEC14496-10 coded picture that was associated with a Rec. ITU-TH.264|ISO/IEC 14496-10 recovery point SEI message withrecovery_frame_cnt equal to 0 and broken_link_flag equal to 1.

Optionally, the external source may also indicate whether the picture isa frame or a field. Then the picture is a field, the external source mayindicate the field parity, such as a top field or a bottom field. If theexternal source does not indicate this, the decoded picture may beinferred to be a frame picture.

Example Flowchart #4

FIG. 7 is a flowchart illustrating a method 700 for coding videoinformation, according to an embodiment of the present disclosure. Thesteps illustrated in FIG. 7 may be performed by an encoder (e.g., thevideo encoder as shown in FIG. 2A or FIG. 2B), a decoder (e.g., thevideo decoder as shown in FIG. 3A or FIG. 3B), or any other component.For convenience, method 700 is described as performed by a coder, whichmay be the encoder, the decoder, or another component.

The method 700 begins at block 701. In block 705, the decoder determinesthat a reference layer is not included in a bitstream. In one example,the reference layer is decoded according to an AVC codec and/oraccording to a non-HEVC codec. In some aspects, the method determineswhether the reference layer is included in the bitstream based upon avalue of a flag or other indicator of the codec. Such a flag or otherindicator may be received from the external source, or may be determinedby the method. In some aspects, the means for determining may include aprocessor. In some aspects, the value may be included in a one of avideo parameter set, a sequence parameter set, a picture parameter set,or an adaptation parameter set.

The decoder then receives, from an external source, a decoded base layerpicture, in block 710. In some aspects, the base layer picture may beassociated with an access unit. In some aspects, the external source mayinclude another decoder. In some aspects, the other decoder may be anAVC decoder. In some aspects, the means for receiving may include aprocessor.

At block 715, the decoder receives, from the external source, anindication that the picture is an IRAP picture. For example, thisindication may include a flag which indicates that the base layerpicture is an IRAP picture. In some aspects, the means for receiving mayinclude a processor. At block 720, the decoder receives a secondindication whether the picture is one of an IDR picture, a CLA picture,or a BLA picture. In some aspects, the means for receiving may include aprocessor. In some aspects, the second indication may be a syntaxelement having three or more possible values. At block 730, the decodercodes the video information based at least in part on the first andsecond indications. In some aspects, the means for decoding may includea processor. The method 700 ends at block 730.

As discussed above, one or more components of video encoder 20 of FIG.2A, video encoder 21 of FIG. 2B, video decoder 30 of FIG. 3A, or videodecoder 31 of FIG. 3B (e.g., inter-layer prediction unit 128 and/orinter-layer prediction unit 166) may be used to implement any of thetechniques discussed in the present disclosure, such as determiningwhether the reference layer codec is the particular type of codec,receiving the decoded base layer picture, storing the decoded base layerpicture, and emptying the memory.

Additional Aspects of Design

Generally, for a current access unit, either no base layer informationis provided by the external source, or the external source must provideat least proscribed set of information. If no information is provided,the base layer picture will not be used for inter-layer prediction forthe current access unit, regardless of whether a base layer picture wasprovided in the access unit in the base layer bitstream. Alternatively,the external source may be proscribed to provide: (1) the decoded samplevalues of the base layer decoded picture, (2) the representation formatof the base layer decoded picture, including the width and height inluma samples, the colour format, the separate colour plane flag, theluma bit depth, and the chroma bit depth, (3) information on whether thebase layer picture is an IRAP picture or not, and if yes, the IRAP NALunit type, which may specify an IDR picture, a CRA picture, or a BLApicture, and optionally, (4) whether the picture is a frame or a field,and when a field, the field parity (a top field or a bottom field). Wheninformation on whether the picture is a frame or a field is notprovided, the decoded picture may be inferred to be a frame picture.

The picture order count of the base layer decoded picture may be setequal to the picture order count of any enhancement layer picture, ifpresent, in the same access unit. Note that in this case, the actualpicture order count of a base layer picture decoded by the base layerdecoder in such a scalable or multiview codec might be different thanthe picture order count value of the same picture when it is decoded byan AVC decoder. When no enhancement layer picture is present for theaccess unit, the base layer decoded picture is not used and can bediscarded.

The base layer decoded picture may be marked as “used for long-termreference.” For CPB operations, the base layer may be considered ashaving zero bits. For DPB operations, only decoded pictures ofenhancement layers may be considered.

When the base layer is non-HEVC, general_profile_space in the firstprofile_tier_level( ) syntax structure in a VPS may be set equal to 1.In this case, the codec type is signaled, and when AVC is indicated, thethree-byte AVC profile and level information is signaled, and the restof the bits in the profile_tier_level( ) syntax structure are allreserved.

When the base layer is non-HEVC, it may be required that the signalingof the three DPB parameters (max sub-DPB size, max reorder, and maxlatency) use the least amount of bits. It may also be required that noneof the hrd_parameters( ) syntax structures apply to layer set 0 (thebase layer only).

When the base layer is non-HEVC, unnecessary signaling for the baselayer in the VPS extension, including VPS VUI, may be avoided, such assub_layers_vps_max_minus1[0], max_tid_il_ref_pics_plus1[0][j], anddirect_dependency_type[i][0].

Additional Code Segments

The following example code segment may be used as part of the VPS VUIsyntax, and may provide for setting or not setting certain flags based,at least in part, on whether a base layer is an HEVC layer:

vps_vui( ){ Descriptor  ...  if( bit_rate_present_vps_flag ||pic_rate_present_vps_flag )   for( i = HevcBaseLayerFlag ? 0 : 1; i <=vps_number_layer_sets_minus1; i++ )    for( j = 0; j <=vps_max_sub_layers_minus1; j++ ) {     if( bit_rate_present_vps_flag )     bit_rate_present_flag[ i ][ j ] u(1)     if(pic_rate_present_vps_flag )      pic_rate_present_flag[ i ][ j ] u(1)    if( bit_rate_present_flag[ i ][ j ] ) {      avg_bit_rate[ i ][ j ]u(16)      max_bit_rate[ i ][ j ] u(16)     }     if(pic_rate_present_flag[ i ][ j ] ) {      constant_pic_rate_idc[ i ][ j ]u(2)      avg_pic_rate[ i ][ j ] u(16)     }    }  tiles_not_in_use_flagu(1)  if( !tiles_not_in_use_flag ) {   for( i = HevcBaseLayerFlag ? 0 :1; i <= MaxLayersMinus1; i++ ) { u(1)    tiles_in_use_flag[ i ]    if(tiles_in_use_flag[ i ] )     loop_filter_not_across_tiles_flag[ i ] u(1)  }   for( i = 1; i <= MaxLayersMinus1; i++ )    for( j = 0; j <NumDirectRefLayers[ layer_id_in_nuh[ i ] ]; j++ ) {     layerIdx =LayerIdxInVps[ RefLayerId[ layer_id_in_nuh[ i ] ][ j ] ]     if(tiles_in_use_flag[ i ] && tiles_in_use_flag[ layerIdx ] )     tile_boundaries_aligned_flag[ i ][ j ] u(1)    }  } wpp_not_in_use_flag  if( !wpp_not_in_use_flag )   for( i =HevcBaseLayerFlag ? 0 : 1; i <= MaxLayersMinus1; i++ )   wpp_in_use_flag[ i ] u(1)  if( HevcBaseLayerFlag ) {  single_layer_for_non_irap_flag u(1)   higher_layer_irap_skip_flag u(1) }  ilp_restricted_ref_layers_flag u(1)  if(ilp_restricted_ref_layers_flag )   for( i = HevcBaseLayerFlag ? 1 : 2; i<= MaxLayersMinus1; i++ )    for( j = 0; j < NumDirectRefLayers[layer_id_in_nuh[ i ] ]; j++ ) {     min_spatial_segment_offset_plus1[ i][ j ] ue(v)     if( min_spatial_segment_offset_plus1[ i ][ j ] > 0) {     ctu_based_offset_enabled_flag[ i ][ j ] u(1)      if(ctu_based_offset_enabled_flag[ i ][ j ] )      min_horizontal_ctu_offset_plus1[ i ][ j ] ue(v)     }    } ... }

The following example code segment may be used as part of the profile,tier and level syntax, and may provide for setting or not settingcertain flags based on a value of general_profile_space (which itselfmay be set based on a codec used for a base layer of a video stream):

profile_tier_level( profilePresentFlag, maxNumSubLayersMinus1 ) {Descriptor  if( profilePresentFlag ) {   general_profile_space u(2)  if( general_profile_space = = 0) {    general_tier_flag u(1)   general_profile_idc u(5)    for( j = 0; j < 32; j++ )    general_profile_compatibility_flag[ j ] u(1)   general_progressive_source_flag u(1)   general_interlaced_source_flag u(1)   general_non_packed_constraint_flag u(1)   general_frame_only_constraint_flag u(1)   general_reserved_zero_44bits u(44)   }  }  if( general_profile_space= = 0) {   general_level_idc u(8)   for( i = 0; i <maxNumSubLayersMinus1; i++ ) {    sub_layer_profile_present_flag[ i ]u(1)    sub_layer_level_present_flag[ i ] u(1)   }   if(maxNumSubLayersMinus1 > 0 )    for( i = maxNumSubLayersMinus1; i < 8;i++ )     reserved_zero_2bits[ i ] u(2)   for( i = 0; i <maxNumSubLayersMinus1; i++ ) {    if( sub_layer_profile_present_flag[ i] ) {     sub_layer_profile_space[ i ] u(2)     sub_layer_tier_flag[ i ]u(1)     sub_layer_profile_idc[ i ] u(5)     for( j = 0; j < 32; j++ )     sub_layer_profile_compatibility_flag[ i ][ j ] u(1)    sub_layer_progressive_source_flag[ i ] u(1)    sub_layer_interlaced_source_flag[ i ] u(1)    sub_layer_non_packed_constraint_flag[ i ] u(1)    sub_layer_frame_only_constraint_flag[ i ] u(1)    sub_layer_reserved_zero_44bits[ i ] u(44)    }    if(sub_layer_level_present_flag[ i ] )     sub_layer_level_idc[ i ] u(8)  }  }  if( general_profile_space = = 1 ) {   base_layer_codec_type u(6)  if( base_layer_codec_type = = 0 )    avc_profile_level_idc u(24)  else    reserved_zero_24bits u(24)   reserved_zero_32bits u(32)  } }

In some aspects, when a first profile_tier_level( ) syntax structure inthe VPS has a general_profile_space flag equal to 0, the variableHevcBaseLayerFlag may be set equal to 1 and the variableAvcBaseLayerFlag may be set equal to 0. For example, the variableHevcBaseLayerFlag may be used to indicate whether the base layer of aparticular video is encoded based upon an HEVC codec or not. Similarly,the variable AvcBaseLayerFlag may be used to indicate whether the baselayer of a particular video is encoded based upon an AVC codec or not.

Alternatively, when the first profile_tier_level( ) syntax structure hasgeneral_profile_space equal to 1 and base later codec type equal to 0,the variable AvcBaseLayerFlag may be set equal to 1, and the variableHevcBaseLayerFlag may be set equal to 0. Further, in this scenario, thevalue of vps_sub_layer_ordering_info_present_flag may be equal to 0 andthe values of vps_max_dec_pic_buffering_minus1[i],vps_max_num_reorder_pics[i], and vps_max_latency_increase_plus1 [i] mayall be equal to 0 for all possible values of i. In this scenario,decoders may be configured to ignore the values ofvps_sub_layer_ordering_info_present_flag,vps_max_dec_pic_buffering_minus1[i], vps_max_num_reorder_pics[i], andvps_max_latency_increase_plus1 [i], and the value ofhrd_layer_set_idx[i] may be greater than 0.

Generally, a vps_extension_offset_flag may specify a byte offset,starting from the beginning of the VPS NAL unit, of the next set offixed-length coded information starting from vps_vui_present_flag, whenpresent, in the VPS NAL unit. When present, emulation prevention bytesthat appear in the VPS NAL unit are counted for purposes of byte offsetidentification.

In some aspects, when the base layer is not coded using an HEVC codec(and therefore, the flag HevcBaseLayerFlag is equal to 0, it may berequired that a value of sps_scaling_list_ref_layer_id shall be greaterthan 0. Generally, sps_scaling_list_ref_layer_id specifies the layer forwhich the active SPS is associated with the same scaling list data asthe current SPS.

Generally, pps_scaling_list_ref_layer_id specifies the layer for whichthe active PPS has the same scaling list data as the current PPS. Thevalue of pps_scaling_list_ref_layer_id shall be in the range of 0 to 62,inclusive. In some aspects, when the base layer of a video is not anHEVC base layer (that is, HevcBaseLayerFlag is equal to 0), it may be arequirement of bitstream conformance for pps_scaling_list_ref_layer_idto be greater than 0.

Profile, Tier and Level Semantics

Generally, when a value of general_profile_space is not provided, thatvalue is inferred to be 0. However, if the value ofgeneral_profile_space is equal to 1, a value of base layer codec typeequal to 0 may specify that the base layer conforms to Rec. ITU-TH.264|ISO/IEC 14496-10. Other values of base layer codec type, in therange of 1 to 63, inclusive, may be reserved for future use byITU-T|ISO/IEC.

Further, avc_base_profile_level_idc may indicate the conformance pointof the Rec. ITU-T H.264|ISO/IEC 14496-10 base layer. For example,avc_base_profile_level_idc may have the same value as the three bytes inRec. ITU-T H.264|ISO/IEC 14496-10 comprised of profile_idc,constraint_set0_flag, constraint_set1_flag, constraint_set2_flag,constraint_set3_flag, constraint_set4_flag, constraint_set5_flag,reserved_zero 2bits, and level_idc of the Rec. ITU-T H.264|ISO/IEC14496-10 sequence parameter set.

Additionally, reserved_zero_24bits and reserved_zero_32bits shall bothbe equal to 0, and other values may be reserved for future use by ITU-TISO/IEC. Decoders may be configured to ignore the values of bothreserved_zero_24bits and reserved_zero_32bits. For example, thefollowing code segment may be used to set values of reserved_zero_24bitsand reserved_zero_32bits when general_profile_space is set to 1:

profile_tier_level( profilePresentFlag, maxNumSubLayersMinus1 ) {Descriptor ...  if( general_profile_space = = 1 ) {  base_layer_codec_type u(6)   if( base_layer_codec_type = = 0 )   avc_profile_level_idc u(24)   else    reserved_zero_24bits u(24)  reserved_zero_32bits u(32)  }General Decoding Process

Generally, when the base layer of a video is an AVC base layer (that is,when AvcBaseLayerFlag is equal to 1), the following applies:

There may be no coded picture with layer ID 0 in the bitstream. This isbecause the base layer is a non-HEVC layer, and so the picture for thebase layer may come from an external source, rather than be included inthe bitstream. The size of the sub-DPB for layer ID 0 is set equal toone.

The values of pic_width_in_luma_samples, pic_height_in_luma_samples,chroma_format_idc, separate colour plane flag, bit_depth_luma_minus8,and bit_depth chroma minus8 for decoded pictures with layer ID 0 areprovided by external source.

For each access unit, a decoded picture with layer ID 0 may be providedby external source. When not provided, no picture with layer ID 0 isused for inter-layer prediction for the current access unit. When such apicture is provided, the picture may also include decoded sample values(1 sample array SL if chroma_format_idc is equal to 0 or 3 sample arraysSL, SCb, and SCr otherwise), the value of the variable BlIrapPicFlag,and when BlIrapPicFlag is equal to 1, the value of nal_unit_type of thedecoded picture. Further, BlIrapPicFlag equal to 1 specifies that thedecoded picture is an IRAP picture. IrapPicFlag equal to 1 specifiesthat the decoded picture is a non-IRAP picture. The provided value ofnal_unit_type of the decoded picture shall be equal to IDR_W_RADL,CRA_NUT, or BLA_W_LP. Generally, a value of nal_unit_type equal toIDR_W_RADL specifies that the decoded picture is an IDR picture and wasdecoded from a Rec. ITU-T H.264|ISO/IEC 14496-10 IDR picture. A value ofnal_unit_type equal to CRA_NUT specifies that the decoded picture is aCRA picture and was decoded from a Rec. ITU-T H.264|ISO/IEC 14496-10coded picture that was associated with a Rec. ITU-T H.264|ISO/IEC14496-10 recovery point SEI message with recovery_frame_cnt equal to 0and broken_link_flag equal to 0. A value of nal_unit_type equal toBLA_W_LP specifies that the decoded picture is a BLA picture and wasdecoded from a Rec. ITU-T H.264|ISO/IEC 14496-10 coded picture that wasassociated with a Rec. ITU-T H.264|ISO/IEC 14496-10 recovery point SEImessage with recovery_frame_cnt equal to 0 and broken_link_flag equalto 1. The external source may optionally indicate whether the picture isa frame or a field, and when a field, the field parity (a top field or abottom field). If not provided, the decoded picture is inferred to be aframe picture.

Generally, the decoded picture with layer ID 0 is stored in the sub-DPBand is marked as “used for long-term reference.” If the access unit hasat least one picture with layer ID greater than 0, the PicOrderCntVal ofthe decoded picture for layer ID 0 is set equal to the PicOrderCntVal ofany picture with layer ID greater than 0 in the access unit. Otherwise,the decoded picture for layer ID 0 is discarded and the sub-DPB forlayer ID 0 is set to be empty. When the access unit has at least onepicture with layer ID greater than 0, after all pictures in the accessunit are decoded, the sub-DPB for the layer with layer ID 0 is set to beempty.

OTHER CONSIDERATIONS

Information and signals disclosed herein may be represented using any ofa variety of different technologies and techniques. For example, data,instructions, commands, information, signals, bits, symbols, and chipsthat may be referenced throughout the above description may berepresented by voltages, currents, electromagnetic waves, magneticfields or particles, optical fields or particles, or any combinationthereof.

The various illustrative logical blocks, modules, circuits, andalgorithm steps described in connection with the embodiments disclosedherein may be implemented as electronic hardware, computer software, orcombinations of both. To clearly illustrate this interchangeability ofhardware and software, various illustrative components, blocks, modules,circuits, and steps have been described above generally in terms oftheir functionality. Whether such functionality is implemented ashardware or software depends upon the particular application and designconstraints imposed on the overall system. Skilled artisans mayimplement the described functionality in varying ways for eachparticular application, but such implementation decisions should not beinterpreted as causing a departure from the scope of the presentinvention.

The techniques described herein may be implemented in hardware,software, firmware, or any combination thereof. Such techniques may beimplemented in any of a variety of devices such as general purposescomputers, wireless communication device handsets, or integrated circuitdevices having multiple uses including application in wirelesscommunication device handsets and other devices. Any features describedas modules or components may be implemented together in an integratedlogic device or separately as discrete but interoperable logic devices.If implemented in software, the techniques may be realized at least inpart by a computer-readable data storage medium comprising program codeincluding instructions that, when executed, performs one or more of themethods described above. The computer-readable data storage medium mayform part of a computer program product, which may include packagingmaterials. The computer-readable medium may comprise memory or datastorage media, such as random access memory (RAM) such as synchronousdynamic random access memory (SDRAM), read-only memory (ROM),non-volatile random access memory (NVRAM), electrically erasableprogrammable read-only memory (EEPROM), FLASH memory, magnetic oroptical data storage media, and the like. The techniques additionally,or alternatively, may be realized at least in part by acomputer-readable communication medium that carries or communicatesprogram code in the form of instructions or data structures and that canbe accessed, read, and/or executed by a computer, such as propagatedsignals or waves.

The program code may be executed by a processor, which may include oneor more processors, such as one or more digital signal processors(DSPs), general purpose microprocessors, an application specificintegrated circuits (ASICs), field programmable logic arrays (FPGAs), orother equivalent integrated or discrete logic circuitry. Such aprocessor may be configured to perform any of the techniques describedin this disclosure. A general purpose processor may be a microprocessor;but in the alternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration. Accordingly, the term “processor,” as used herein mayrefer to any of the foregoing structure, any combination of theforegoing structure, or any other structure or apparatus suitable forimplementation of the techniques described herein. In addition, in someaspects, the functionality described herein may be provided withindedicated software modules or hardware modules configured for encodingand decoding, or incorporated in a combined video encoder-decoder(CODEC). Also, the techniques could be fully implemented in one or morecircuits or logic elements.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses, including a wireless handset, an integratedcircuit (IC) or a set of ICs (e.g., a chip set). Various components,modules, or units are described in this disclosure to emphasizefunctional aspects of devices configured to perform the disclosedtechniques, but do not necessarily require realization by differenthardware units. Rather, as described above, various units may becombined in a codec hardware unit or provided by a collection ofinter-operative hardware units, including one or more processors asdescribed above, in conjunction with suitable software and/or firmware.

Various embodiments of the invention have been described. These andother embodiments are within the scope of the following claims.

What is claimed is:
 1. A method of decoding video information via a H.265/High Efficiency Video Coding (HEVC) decoder, the method comprising: receiving, via a receiver, one or more video blocks of one or more coded pictures associated with one or more enhancement layers based on a H.265/HEVC standard and a multi-layer extension thereof; determining, via a processor of the H.265/HEVC decoder, that the one or more video blocks do not belong to coded pictures associated with a base layer, wherein the base layer is decoded according to a H.264/Advanced Video Coding (AVC) codec; receiving, via the receiver and from an external source that is external to the H.265/HEVC decoder, a decoded base layer picture; receiving, via the receiver and from the external source, a flag that indicates whether the decoded base layer picture is an intra random access point (IRAP) picture; based on the flag indicating that the decoded base layer picture is an IRAP picture, receiving, via the receiver and from the external source, a value of a Network Abstraction Layer (NAL) unit type of the decoded base layer picture, wherein the value of the NAL unit type of the decoded base layer picture is required to be equal to one of IDR_W_RADL, CRA_NUT, and BLA_W_LP, and wherein: the value of the NAL unit type of the decoded base layer picture being equal to IDR_W_RADL specifies that the decoded base layer picture is an instantaneous decoder refresh (IDR) picture and was decoded from a H.264/AVC IDR picture, the value of the NAL unit type of the decoded base layer picture being equal to CRA_NUT specifies that the decoded base layer picture is a clean random access (CRA) picture and was decoded from a H.264/AVC coded picture that was associated with a H.264/AVC recovery point SEI message with recovery_frame_cnt equal to 0 and broken_link_flag equal to 0, and the value of the NAL unit type of the decoded base layer picture being equal to BLA_W_LP indicates that the decoded base layer picture is a broken link access (BLA) picture and was decoded from a H.264/AVC coded picture that was associated with a H.264/AVC recovery point SEI message with recovery_frame_cnt equal to 0 and broken_link_flag equal to 1; decoding, via the processor, the one or more coded pictures based at least in part on the flag and the NAL unit type of the decoded base layer picture received from the external source; and displaying the decoded one or more coded pictures on a display device.
 2. The method of claim 1, wherein said determining that the received one or more video blocks do not belong to coded pictures associated with the base layer is based upon a value included in one of a video parameter set (VPS), a sequence parameter set (SPS), a picture parameter set (PPS), or an adaptation parameter set (APS).
 3. The method of claim 1, wherein the external source is a second decoder.
 4. The method of claim 1, wherein the flag has a value of either 1 or 0 to indicate that the decoded base layer picture is the IRAP picture.
 5. An apparatus configured to decode video information, the apparatus comprising: a memory configured to store information associated with one or more video blocks of one or more coded pictures associated with one or more enhancement layers based on a H.265/High Efficiency Video Coding (HEVC) standard and a multi-layer extension thereof; and a receiver in communication with the memory, the receiver configured to: receive the one or more video blocks; receive, from an external source that is external to a H.265/HEVC decoder, a decoded base layer picture; receive, from the external source, a flag that indicates whether the decoded base layer picture is an intra random access point (IRAP) picture; based on the flag indicating that the decoded base layer picture is an IRAP picture, receive, from the external source, a value of a Network Abstraction Layer (NAL) unit type of the decoded base layer picture, wherein the value of the NAL unit type of the decoded base layer picture is required to be equal to one of IDR_W_RADL, CRA_NUT, and BLA_W_LP, and wherein: the value of the NAL unit type of the decoded base layer picture being equal to IDR_W_RADL specifies that the decoded base layer picture is an instantaneous decoder refresh (IDR) picture and was decoded from a H.264/Advanced Video Coding (AVC) picture, the value of the NAL unit type of the decoded base layer picture being equal to CRA_NUT specifies that the decoded base layer picture is a clean random access (CRA) picture and was decoded from a H.264/AVC coded picture that was associated with a H.264/AVC recovery point SEI message with recovery_frame_cnt equal to 0 and broken_link_flag equal to 0, a the value of the NAL unit type of the decoded base layer picture being equal to BLA_W_LP indicates that the decoded base layer picture is a broken link access (BLA) picture and was decoded from a H.264/AVC coded picture that was associated with a H.264/AVC recovery point SEI message with recovery_frame_cnt equal to 0 and broken_link_flag equal to 1; and a processor of the H.265/HEVC decoder in communication with the memory and the receiver, the processor configured to: determine that the one or more video blocks do not include coded pictures associated with a base layer, wherein the base layer is decoded according to an H.264/AVC codec; decode the one or more coded pictures based at least in part on the flag and the NAL unit type of the decoded base layer picture received from the external source; and display the decoded one or more pictures on a display device.
 6. The apparatus of claim 5, wherein the determination that the one or more video blocks do not belong to coded pictures associated with the base layer is based upon a value included in one of a video parameter set (VPS), a sequence parameter set (SPS), a picture parameter set (PPS), or an adaptation parameter set (APS).
 7. The apparatus of claim 5, wherein the external source is a second decoder.
 8. The apparatus of claim 5, wherein the flag has a value of either 1 or 0 to indicate that the decoded base layer picture is the IRAP picture.
 9. A non-transitory computer readable medium comprising code that, when executed, causes an apparatus to: receive, via a receiver, one or more video blocks of one or more coded pictures associated with one or more enhancement layers based on a H.265/High Efficiency Video Coding (HEVC) standard and a multi-layer extension thereof; determine, via a processor, that the one or more video blocks do not belong to coded pictures associated with a base layer, wherein the base layer is decoded according to a H.264/Advanced Video Coding (AVC) codec; receive, via the receiver and from an external source that is external to the apparatus, a decoded base layer picture; receive, via the receiver and from the external source, a flag that indicates whether the decoded base layer picture is an intra random access point (IRAP) picture; based on the flag indicating that the decoded base layer picture is an IRAP picture, receive, via the receiver and from the external source, a value of a Network Abstraction Layer (NAL) unit type of the decoded base layer picture, wherein the value of the NAL unit type of the decoded base layer picture is required to be equal to one of IDR_W_RADL, CRA_NUT, and BLA_W_LP, and wherein: the value of the NAL unit type of the decoded base layer picture being equal to IDR_W_RADL specifies that the decoded base layer picture is an instantaneous decoder refresh (IDR) picture and was decoded from a H.264/AVC IDR picture, the value of the NAL unit type of the decoded base layer picture being equal to CRA_NUT specifies that the decoded base layer picture is a clean random access (CRA) picture and was decoded from a H.264/AVC coded picture that was associated with a H.264/AVC recovery point SEI message with recovery_frame_cnt equal to 0 and broken_link_flag equal to 0, and the value of the NAL unit type of the decoded base layer picture being equal to BLA_W_LP indicates that the decoded base layer picture is a broken link access (BLA) picture and was decoded from a H.264/AVC coded picture that was associated with a H.264/AVC recovery point SEI message with recovery_frame_cnt equal to 0 and broken_link_flag equal to 1; decode, via the processor, the one or more coded pictures based at least in part on the flag and the NAL unit type of the decoded base layer picture received from the external source; and display the decoded one or more pictures on a display device.
 10. The non-transitory computer readable medium of claim 9, wherein the external source is a second decoder.
 11. The non-transitory computer readable medium of claim 9, wherein the flag has a value of either 1 or 0 to indicate that the decoded base layer picture is the IRAP picture.
 12. A video decoding device configured to decode video information, the video decoding device comprising: means for receiving one or more video blocks of one or more coded pictures associated with one or more enhancement layers based on a H.265/High Efficiency Video Coding (HEVC) standard and a multi-layer extension thereof; means for determining that the one or more video blocks do not belong to coded pictures associated with a base layer, wherein the base layer is decoded according to a H.264/Advanced Video Coding (AVC) codec; means for receiving a decoded base layer picture from an external source that is external to the video decoding device; means for receiving, from the external source, a flag that indicates whether the decoded base layer picture is an intra random access point (IRAP) picture; means for receiving, based on the flag indicating that the decoded base layer picture is an IRAP picture, a value of a Network Abstraction Layer (NAL) unit type of the decoded base layer picture, wherein the value of the NAL unit type of the decoded base layer picture is required to be equal to one of IDR_W_RADL, CRA_NUT, and BLA_W_LP, and wherein: the value of the NAL unit type of the decoded base layer picture being equal to IDR_W_RADL specifies that the decoded base layer picture is an instantaneous decoder refresh (IDR) picture and was decoded from a H.264/AVC IDR picture, the value of the NAL unit type of the decoded base layer picture being equal to CRA_NUT specifies that the decoded base layer picture is a clean random access (CRA) picture and was decoded from a H.264/AVC coded picture that was associated with a H.264/AVC recovery point SEI message with recovery_frame_cnt equal to 0 and broken_link_flag equal to 0, and the value of the NAL unit type of the decoded base layer picture being equal to BLA_W_LP indicates that the decoded base layer picture is a broken link access (BLA) picture and was decoded from a H.264/AVC coded picture that was associated with a H.264/AVC recovery point SEI message with recovery_frame_cnt equal to 0 and broken_link_flag equal to 1; means for decoding the one or more coded pictures based at least in part on the flag and the NAL unit type of the decoded base layer picture received from the external source; and means for displaying the decoded one or more pictures.
 13. The video decoding device of claim 12, wherein the external source is a second decoder.
 14. The video decoding device of claim 12, wherein the flag has a value of either 1 or 0 to indicate that the decoded base layer picture is the IRAP picture. 